Cellulose esters and their production in halogenated ionic liquids

ABSTRACT

Ionic liquids and cellulose ester compositions and processes for producing ionic liquids and cellulose esters. Cellulose esters can be produced by esterifying cellulose in a reaction medium comprising one or more halide ionic liquids and at least one binary component. Cellulose esters prepared via the methods of the present invention can have a degree of substitution (“DS”) of at least 1.5 and can comprise a plurality of ester substituents, where at least 50 percent of the ester substituents comprise alkyl esters having a carbon chain length of at least 6 carbons.

RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Pat.App. Ser. No. 61/028,280, titled “CELLULOSE ESTERS AND THEIR PRODUCTIONIN HALOGENATED IONIC LIQUIDS,” filed Feb. 13, 2008, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to cellulose esters and/or ionicliquids. One aspect of the invention concerns processes for producingcellulose esters in ionic liquids.

2. Description of the Related Art

Cellulose is a β-1,4-linked polymer of anhydroglucose. Cellulose istypically a high molecular weight, polydisperse polymer that isinsoluble in water and virtually all common organic solvents. The use ofunmodified cellulose from wood or cotton products, such as in thehousing or fabric industries, is well known. Unmodified cellulose isalso utilized in a variety of other applications usually as a film(e.g., cellophane), as a fiber (e.g., viscose rayon), or as a powder(e.g., microcrystalline cellulose) used in pharmaceutical applications.Modified cellulose, including cellulose esters, are also utilized in awide variety of commercial applications. Cellulose esters can generallybe prepared by first converting cellulose to a cellulose triester, thenhydrolyzing the cellulose triester in an acidic aqueous media to thedesired degree of substitution (“DS”), which is the average number ofester substituents per anhydroglucose monomer. Hydrolysis of cellulosetriesters containing a single type of acyl substituent under theseconditions can yield a random copolymer that can comprise up to 8different monomers depending upon the final DS.

Ionic liquids (“ILs”) are liquids containing substantially only anionsand cations. Room temperature ionic liquids (“RTILs”) are ionic liquidsthat are in liquid form at standard temperature and pressure. Thecations associated with ILs are structurally diverse, but generallycontain one or more nitrogens that are part of a ring structure and canbe converted to a quaternary ammonium. Examples of these cations includepyridinum, pyridazinium, pyrimidinium, pyrazinium, imidazolium,pyrazolium, oxazolium, triazolium, thiazolium, piperidinium,pyrrolidinium, quinolinium, and isoquinolinium. The anions associatedwith ILs can also be structurally diverse and can have a significantimpact on the solubility of the ILs in different media. For example, ILscontaining hydrophobic anions such as hexafluorophosphates ortriflimides have very low solubilities in water, while ILs containinghydrophilic anions such chloride or acetate are completely miscible inwater.

The names of ionic liquids can generally be abbreviated according to thefollowing convention. Alkyl cations are often named by the first lettersof the alkyl substituents and the cation, which are given within a setof brackets, followed by an abbreviation for the anion. Although notexpressively written, it should be understood that the cation has apositive charge and the anion has a negative charge. For example,[BMIm]OAc indicates 1-butyl-3-methylimidazolium acetate, [AMIm]Clindicates 1-allyl-3-methylimidazolium chloride, and [EMIm]OF indicates1-ethyl-3-methylimidazolium formate.

Ionic liquids can be costly; thus, use of ionic liquids as solvents inmany processes may not be feasible. Despite this, methods and apparatusfor reforming and/or recycling ionic liquids have heretofore beeninsufficient. Furthermore, many processes for producing ionic liquidsinvolve the use of halide and/or sulfur intermediates, or the use ofmetal oxide catalysts. Such processes can produce ionic liquids havinghigh levels of residual metals, sulfur, and/or halides.

SUMMARY OF THE INVENTION

One embodiment of the present invention concerns a process for making acellulose ester. The process of this embodiment comprises (a)introducing a reaction medium comprising cellulose, a halide ionicliquid and a binary component into an esterification zone; and (b)combining at least one acylating reagent with the reaction medium in theesterification zone to esterify at least a portion of the cellulosethereby producing the cellulose ester.

Another embodiment of the present invention concerns a process formaking cellulose esters. The process of this embodiment comprises (a)dissolving a cellulose in a halide ionic liquid to thereby form aninitial cellulose solution; (b) contacting the initial cellulosesolution with a binary component and an acylating reagent underconditions sufficient to provide an acylated cellulose solutioncomprising a cellulose ester; (c) contacting the acylated cellulosesolution with a non-solvent to cause at least a portion of the celluloseester to precipitate and thereby provide a slurry comprisingprecipitated cellulose ester and at least a portion of the halide ionicliquid; (d) separating at least a portion of said precipitated celluloseester from said halide ionic liquid to thereby provide a recoveredcellulose ester and a separated halide ionic liquid; and (e) recyclingat least a portion of the separated halide ionic liquid for use indissolving additional cellulose.

Still another embodiment of the present invention concerns a compositioncomprising a cellulose ester having a degree of substitution (“DS”) ofat least 1.5 and comprising a plurality of ester substituents, where atleast 50 percent of the ester substituents comprise alkyl esters havinga carbon chain length of at least 6 carbons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram depicting the major steps involved in aprocess for producing cellulose esters in ionic liquids;

FIG. 2 is a more detailed diagram of a process for producing celluloseesters, depicting a number of additional/optional steps for enhancingthe overall efficacy and/or efficiency of the production process;

FIG. 3 is a plot of absorbance versus time showing the dissolution of 5weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 4 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 5 molarequivalents of acetic anhydride;

FIG. 5 is a plot of absorbance versus time showing the dissolution of 5weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 6 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride at 80° C.;

FIG. 7 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 80° C.;

FIG. 8 is a plot of absorbance versus time showing the dissolution of 5weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 9 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 80° C.;

FIG. 10 is a plot of absorbance versus time showing the dissolution of10 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 11 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 80° C.;

FIG. 12 is a plot of absorbance versus time showing the dissolution of15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 13 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 100° C.;

FIG. 14 is a plot of absorbance versus time showing the dissolution of15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride and3 weight percent acetic acid;

FIG. 15 depicts the proton NMR spectra of a cellulose acetate preparedby direct acetylation before and after randomization;

FIG. 16 is plot of weight percent acetic acid versus time for theesterification of acetic acid, as determined by infrared spectroscopy;

FIG. 17 is a plot of absorbance versus time showing the removal of waterfrom 1-butyl-3-methylimidazolium acetate prior to dissolution ofcellulose;

FIG. 18 is a plot of absorbance versus time showing the dissolution of10 weight percent cellulose in 1-butyl-3-methylimidazolium acetate and0.1 molar equivalents of zinc acetate at room temperature;

FIG. 19 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium acetate with 5 molarequivalents of acetic anhydride and 0.1 molar equivalents of zincacetate;

FIG. 20 is a spectral analysis showing infrared spectra of1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazoliumacetate upon first and second additions of 0.5 molar equivalents ofacetic anhydride;

FIG. 21 is a plot of relative concentration versus time for1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazoliumacetate upon first and second additions of 0.5 molar equivalents ofacetic anhydride;

FIG. 22 is spectral analysis showing infrared spectra of1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazoliumacetate, and a spectrum after 1 equivalent of acetic anhydride has beenadded to the 1-butyl-3-methylimidazolium formate in the presence of 2molar equivalents of methanol;

FIG. 23 is a plot of relative concentration versus time for1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazoliumacetate upon addition of 2 molar equivalents of methanol and then uponaddition of 1 equivalent of acetic anhydride;

FIG. 24 is a plot of absorbance versus time showing the dissolution ofwater-wet cellulose in 1-butyl-3-methylimidazolium acetate at 80° C.

FIG. 25 is a plot of absorbance versus time showing the esterificationof water-wet cellulose dissolved in 1-butyl-3-methylimidazolium acetate;

FIG. 26 is a spectral analysis showing the ring proton resonances ofcellulose acetates prepared from cellulose dissolved in1-butyl-3-methylimidazolium acetate (top spectrum), and the ring protonresonances of cellulose acetates prepared from cellulose dissolved in1-butyl-3-methylimidazolium chloride (bottom spectrum);

FIG. 27 is a spectral analysis showing the ring proton resonances ofcellulose acetates prepared from cellulose dissolved in1-butyl-3-methylimidazolium acetate after water addition (top spectrum)and before water addition (bottom spectrum);

FIG. 28 is a plot of viscosity versus frequency showing the viscositiesof various solutions of 5 weight percent cellulose dissolved in1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazoliumchloride with 5 weight percent acetic acid, and1-butyl-3-methylimidazolium chloride with 10 weight percent acetic acidat 25, 50, 75, and 100° C.;

FIG. 29 is a plot of viscosity versus frequency that compares theviscosity of 1-butyl-3-methylimidazolium chloride containing noco-solvent with the viscosity of 1-butyl-3-methylimidazolium chloridecontaining methyl ethyl ketone as a co-solvent; and

FIG. 30 is a plot of absorbance versus time comparing the degree ofsubstitution and reaction rates during esterification of cellulosedissolved in 1-butyl-3-methylimidazolium propionate versus dissolved in1-butyl-3-methylimidazolium propionate containing 11.9 weight percentpropionic acid.

DETAILED DESCRIPTION

FIG. 1 depicts a simplified system for producing cellulose esters. Thesystem of FIG. 1 generally includes a dissolution zone 20, anesterification zone 40, a cellulose ester recovery/treatment zone 50,and an ionic liquid recovery/treatment zone 60.

As shown in FIG. 1, cellulose and an ionic liquid can be fed todissolution zone 20 via lines 62 and 64, respectively. In dissolutionzone 20, the cellulose can be dissolved to form an initial cellulosesolution comprising the cellulose and the ionic liquid. The initialcellulose solution can then be transported to esterification zone 40. Inesterification zone 40, a reaction medium comprising the dissolvedcellulose can be subjected to reaction conditions sufficient to at leastpartially esterify the cellulose, thereby producing an initial celluloseester. An acylating reagent can be added to esterification zone 40and/or dissolution zone 20 to help facilitate esterification of thedissolved cellulose in esterification zone 40.

As illustrated in FIG. 1, an esterified medium can be withdrawn fromesterification zone 40 via line 80 and thereafter transported tocellulose ester recovery/treatment zone 50 where the initial celluloseester can be recovered and treated to thereby produce a final celluloseester that can exit recovery/treatment zone 50 via line 90. A recyclestream can be produced from cellulose ester recovery/treatment zone 50via line 86. This recycle stream can comprise an altered ionic liquidderived from the ionic liquid originally introduced into dissolutionzone 20. The recycle stream in line 86 can also include various othercompounds including byproducts of reactions occurring in upstream zones20,40,50 and/or additives employed in upstream zones 20,40,50. Therecycle stream in line 86 can be introduced into ionic liquidrecovery/treatment zone 60 where it can be subjected to separationand/or reformation processes. A recycled ionic liquid can be producedfrom ionic liquid recovery/treatment zone 60 and can be routed back todissolution zone 20 via line 70. Additional details of the streams,reactions, and steps involved in the cellulose ester production systemof FIG. 1 are provided immediately below.

As mentioned above, cellulose can be fed to dissolution zone 20 via line62. The cellulose fed to dissolution zone 20 can be any cellulose knownin the art that is suitable for use in the production of celluloseesters. In one embodiment, the cellulose suitable for use in the presentinvention can be obtained from soft or hard woods in the form of woodpulps, or from annual plants such as cotton or corn. The cellulose canbe a β-1,4-linked polymer comprising a plurality of anhydroglucosemonomer units. The cellulose suitable for use in the present inventioncan generally comprise the following structure:

Additionally, the cellulose employed in the present invention can havean α-cellulose content of at least about 90 percent by weight, at leastabout 95 percent by weight, or at least 98 percent by weight.

The cellulose fed to dissolution zone 20 can have a degree ofpolymerization (“DP”) of at least about 10, at least about 250, at leastabout 1,000, or at least 5,000. As used herein, the term “degree ofpolymerization,” when referring to cellulose and/or cellulose esters,shall denote the average number of anhydroglucose monomer units percellulose polymer chain. Furthermore, the cellulose fed to dissolutionzone 20 can have a weight average molecular weight in the range of fromabout 1,500 to about 850,000, in the range of from about 40,000 to about200,000, or in the range of from 55,000 to 160,000. Additionally, thecellulose suitable for use in the present invention can be in the formof a sheet, hammer milled sheet, fiber, or powder. In one embodiment,the cellulose can be a powder having a mean average particle size ofless than about 500 micrometers (“μm”), less than about 400 μm, or lessthan 300 μm.

As mentioned above, an ionic liquid can be fed to dissolution zone 20via line 64. The ionic liquid fed to dissolution zone 20 can be anyionic liquid capable of at least partially dissolving cellulose. As usedherein, the term “ionic liquid” shall denote any substance containingsubstantially only ions, and which has a melting point at a temperatureof 200° C. or less. In one embodiment, the ionic liquid suitable for usein the present invention can be a cellulose dissolving ionic liquid. Asused herein, the term “cellulose dissolving ionic liquid” shall denoteany ionic liquid capable of dissolving cellulose in an amount sufficientto create an at least 0.1 weight percent cellulose solution. In oneembodiment, the ionic liquid fed to dissolution zone 20 via line 64 canhave a temperature at least 10° C. above the melting point of the ionicliquid. In another embodiment, the ionic liquid can have a temperaturein the range of from about 0 to about 100° C., in the range of fromabout 20 to about 80° C., or in the range of from 25 to 50° C.

In one embodiment, the ionic liquid fed to dissolution zone 20 via line64 can additionally comprise water, nitrogen-containing bases, alcohol,and/or carboxylic acid. The ionic liquid in line 64 can comprise lessthan about 15 weight percent, less than about 5 weight percent, or lessthan 2 weight percent of each of water, nitrogen-containing bases,alcohol, and carboxylic acid.

As mentioned above, an ionic liquid comprises ions. These ions includeboth cations (i.e., positively charged ions) and anions (i.e.,negatively charged ions). In one embodiment, the cations of the ionicliquid suitable for use in the present invention can include, but arenot limited to, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium,1,2,3-triazolium, and/or thiazolium cations, which correspond to thefollowing structures:

In the above structures, R₁ and R₂ can independently be a C₁ to C₈ alkylgroup, a C₂ to C₈ alkenyl group, or a C₁ to C₈ alkoxyalkyl group. R₃,R₄, and R₅ can independently be a hydrido, a C₁ to C₈ alkyl group, a C₂to C₈ alkenyl group, a C₁ to C₈ alkoxyalkyl group, or a C₁ to C₈ alkoxygroup. In one embodiment, the cation of the ionic liquid used in thepresent invention can comprise an alkyl substituted imidazolium cation,where R₁ is a C₁ to C₄ alkyl group, and R₂ is a different C₁ to C₄ alkylgroup.

In one embodiment of the present invention, the cellulose dissolvingionic liquid can be a carboxylated ionic liquid. As used herein, theterm “carboxylated ionic liquid” shall denote any ionic liquidcomprising one or more carboxylate anions. Carboxylate anions suitablefor use in the carboxylated ionic liquids of the present inventioninclude, but are not limited to, C₁ to C₂₀ straight- or branched-chain,substituted or unsubstituted carboxylate anions. Examples of suitablecarboxylate anions for use in the carboxylated ionic liquid include, butare not limited to, formate, acetate, propionate, butyrate, valerate,hexanoate, lactate, oxalate, or chloro-, bromo-, fluoro-substitutedacetate, propionate, or butyrate, and the like. In one embodiment, theanion of the carboxylated ionic liquid can be a C₂ to C₆ straight-chaincarboxylate. Furthermore, the anion can be acetate, propionate,butyrate, or a mixture of acetate, propionate, and/or butyrate. Specificexamples of carboxylated ionic liquids suitable for use in the presentinvention include, but are not limited t, 1-ethyl-3-methylimidazoliumacetate, 1-ethyl-3-methylimidazolium propionate,1-ethyl-3-methylimidazolium butyrate, 1-butyl-3-methylimidazoliumacetate, 1-butyl-3-methylimidazolium propionate,1-butyl-3-methylimidazolium butyrate, or mixtures thereof.

In one embodiment of the present invention, the carboxylated ionicliquid can contain sulfur in an amount less than 200 parts per millionby weight (“ppmw”), less than 100 ppmw, less than 50 ppmw, or less than10 ppmw based on the total weight of the ion content of the carboxylatedionic liquid. Additionally, the carboxylated ionic liquid can contain atotal halide content of less than 200 ppmw, less than 100 ppmw, lessthan 50 ppmw, or less than 10 ppmw based on the total weight of the ioncontent of the carboxylated ionic liquid. Furthermore, the carboxylatedionic liquid can contain a total metal content of less than 200 ppmw,less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on thetotal weight of the ion content of the carboxylated ionic liquid. In oneembodiment, the carboxylated ionic liquid can contain transition metalsin an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw,or less than 10 ppmw based on the total weight of the ion content of thecarboxylated ionic liquid. The sulfur, halide, and metal content of thecarboxylated ionic liquid can be determined by x-ray fluorescence(“XRF”) spectroscopy.

The carboxylated ionic liquid of the present invention can be formed byany process known in the art for making ionic liquids having at leastone carboxylate anion. In one embodiment, the carboxylated ionic liquidof the present invention can be formed by first forming an intermediateionic liquid. The intermediate ionic liquid can be any known ionicliquid, at least a portion of whose ions can participate in an anionexchange reaction. In one embodiment, the intermediate ionic liquid cancomprise a plurality of cations such as those described above withreference to the cellulose dissolving ionic liquid (e.g., imidazolium,pyrazolium, oxazolium, 1,2,3,-triazolium, 1,2,4-triazolium, orthiazolium). In one embodiment, the cation of the intermediate ionicliquid can comprise 1-ethyl-3-methylimidazolium or1-butyl-3-methylimidazolium. Additionally, the intermediate ionic liquidcan comprise a plurality of anions. In one embodiment, the intermediateionic liquid can comprise a plurality of carboxylate anions, such as,for example, formate, acetate, and/or propionate anions.

In one embodiment, the intermediate ionic liquid of the presentinvention can comprise an alkyl amine formate. The amine cation of thealkyl amine formate can comprise any of the above-described substitutedor unsubstituted imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium,1,2,3-triazolium, and/or thiazolium cations. In one embodiment, theamine of the alkyl amine formate can be an alkyl substitutedimidazolium, alkyl substituted pyrazolium, alkyl substituted oxazolium,alkyl substituted triazolium, alkyl substituted thiazolium, and mixturesthereof. In one embodiment, the amine of the alkyl amine formate can bean alkyl substituted imidazolium. Examples of alkyl amine formatessuitable for use as an intermediate ionic liquid in the presentinvention include, but are not limited to, 1-methyl-3-methylimidazoliumformate, 1-ethyl-3-methylimidazolium formate,1-propyl-3-methylimidazolium formate, 1-butyl-3-methylimidazoliumformate, 1-pentyl-3-methylimidazolium formate, and/or1-octyl-3-methylimidazolium formate.

The intermediate ionic liquid useful in the present invention can beformed by contacting at least one amine with at least one alkyl formate.Amines suitable for use in the present invention include, but are notlimited to, substituted or unsubstituted imidazoles, pyrazoles,oxazoles, triazoles, and/or thiazoles. In one embodiment, the alkylamine formate can be formed by contacting at least one alkyl substitutedimidazole with at least one alkyl formate. Examples of alkyl substitutedimidazoles suitable for use in forming the intermediate ionic liquidinclude, but are not limited to, 1-methylimidazole, 1-ethylimidazole,1-propylimidazole, 1-butylimidazole, 1-hexylimidazole, and/or1-octylimidazole. Examples of alkyl formates suitable for use in formingthe intermediate ionic liquid include, but are not limited to, methylformate, ethyl formate, propyl formate, isopropyl formate, butylformate, isobutyl formate, tert-butyl formate, hexyl formate, octylformate, and the like. In one embodiment, the alkyl formate used informing the intermediate ionic liquid can comprise methyl formate.

Once the intermediate ionic liquid has been formed, the intermediateionic liquid can be contacted with one or more carboxylate anion donorsat a contact time, pressure, and temperature sufficient to cause the atleast partial conversion of the intermediate ionic liquid to at leastone of the above-mentioned carboxylated ionic liquids. Such conversioncan be accomplished via anion exchange between the carboxylate aniondonor and the intermediate ionic liquid. In one embodiment, at least aportion of the formate of the alkyl amine formate can be replaced viaanion exchange with a carboxylate anion originating from one or morecarboxylate anion donors.

Carboxylate anion donors useful in the present invention can include anysubstance capable of donating at least one carboxylate anion. Examplesof carboxylate anion donors suitable for use in the present inventioninclude, but are not limited to, carboxylic acids, anhydrides, and/oralkyl carboxylates. In one embodiment, the carboxylate anion donor cancomprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or arylcarboxylic acids, anhydrides, or methyl esters. Additionally, thecarboxylate anion donor can comprise one or more C₂ to C₁₂straight-chain alkyl carboxylic acids, anhydrides, or methyl esters.Furthermore, the carboxylate anion donor can comprise one or more C₂ toC₄ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters.In one embodiment, the carboxylate anion donor can comprise at least oneanhydride, which can comprise acetic anhydride, propionic anhydride,butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoicanhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauricanhydride, palmitic anhydride, stearic anhydride, benzoic anhydride,substituted benzoic anhydrides, phthalic anhydride, isophthalicanhydride, and mixtures thereof.

The amount of carboxylate anion donor useful in the present inventioncan be any amount suitable to convert at least a portion of theintermediate ionic liquid to a carboxylated ionic liquid. In oneembodiment, the carboxylate anion donor can be present in a molar ratiowith the intermediate ionic liquid in the range of from about 1:1 toabout 20:1 carboxylate anion donor-to-intermediate ionic liquid anioncontent, or in the range of from 1:1 to 6:1 carboxylate aniondonor-to-intermediate ionic liquid anion content. In one embodiment,when alkyl amine formate is present as the intermediate ionic liquids,the carboxylate anion donor can be present in an amount in the range offrom 1 to 20 molar equivalents per alkyl amine formate, or in the rangeof from 1 to 6 molar equivalents per alkyl amine formate.

The anion exchange between the intermediate ionic liquid and thecarboxylate anion donor can be accomplished in the presence of at leastone alcohol. Alcohols useful in the present invention include, but arenot limited to, alkyl or aryl alcohols such as methanol, ethanol,n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol, and thelike. In one embodiment, the alcohol can be methanol. The amount ofalcohol present in the contact mixture during conversion of theintermediate ionic liquid can be in the range of from about 0.01 toabout 20 molar equivalents of the ionic liquid, or in the range of from1 to 10 molar equivalents of the ionic liquid.

In one embodiment, water can be present in the contact mixture duringthe anion exchange between the intermediate ionic liquid and thecarboxylate anion donor. The amount of water present in the contactmixture during conversion of the intermediate ionic liquid can be in therange of from about 0.01 to about 20 molar equivalents of the ionicliquid, or in the range of from 1 to 10 molar equivalents of the ionicliquid.

As mentioned above, the conversion of the intermediate ionic liquid tothe carboxylated ionic liquid can be performed at a contact time,pressure, and temperature sufficient to cause the at least partialconversion of the intermediate ionic liquid to the carboxylated ionicliquid. In one embodiment, the conversion can be performed for a time inthe range of from about 1 minute to about 24 hours, or in the range offrom 30 minutes to 18 hours. Additionally, the conversion can beperformed at a pressure up to 21,000 kPa, or up to 10,000 kPa. In oneembodiment, the conversion can be performed at a pressure in the rangeof from about 100 to about 21,000 kPa, or in the range of from 100 to10,000 kPa. Furthermore, the conversion can be performed at atemperature in the range of from about 0 to about 200° C., or in therange of from 25 to 170° C.

In one embodiment, the resulting carboxylated ionic liquid can comprisecarboxylate anions comprising substituted or unsubstituted C₁ to C₂₀straight- or branched-chain carboxylate anions. In one embodiment, thecarboxylate anions can comprise C₂ to C₆ straight-chain carboxylateanions. Additionally, the carboxylated ionic liquid can comprisecarboxylate anions such as, for example, formate, acetate, propionate,butyrate, valerate, hexanoate, lactate, and/or oxalate anions. In oneembodiment, the carboxylated ionic liquid can comprise at least 50percent carboxylate anions, at least 70 percent carboxylate anions, orat least 90 percent carboxylate anions. In another embodiment, thecarboxylated ionic liquid can comprise at least 50 percent acetateanions, at least 70 percent acetate anions, or at least 90 percentacetate anions.

In an alternative embodiment of the present invention, theabove-mentioned cellulose dissolving ionic liquid can be a halide ionicliquid. As used herein, the term “halide ionic liquid” shall denote anyionic liquid that contains at least one halide anion. In one embodiment,the halide anions of the halide ionic liquid can comprise fluoride,chloride, bromide, and/or iodide. In another embodiment, the halideanions can be chloride and/or bromide. Additionally, as mentioned above,the cations of the cellulose dissolving ionic liquid can include, butare not limited to, imidazolium, pyrazolium, oxazolium,1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations. Anymethod known in the art suitable for making a halide ionic liquid can beemployed in the present invention. Examples of halide ionic liquidssuitable for use in the present invention include, but are not limitedto, 1-butyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazoliumchloride, 1-ethyl-3-methylimidazolium chloride,1-allyl-3-methylimidazolium chloride, or mixtures thereof.

Referring again to FIG. 1, the amount of cellulose fed to dissolutionzone 20 can be in the range of from about 1 to about 40 weight percent,in the range of from about 5 to about 25 weight percent, or in the rangeof from 10 to 20 weight percent based on the combined weight ofcellulose and the total amount of ionic liquid fed to dissolution zone20. In one embodiment, the resulting medium formed in dissolution zone20 (a.k.a., the dissolution medium) can comprise other components, suchas, for example, water, alcohol, acylating reagents, and/or carboxylicacids. In one embodiment, the medium formed in dissolution zone 20 cancomprise water in an amount in the range of from about 0.001 to about200 weight percent, in the range of from about 1 to about 100 weightpercent, or in the range of from 5 to 15 weight percent based on theentire weight of all other components in the medium formed indissolution zone 20. Additionally, the medium formed in dissolution zone20 can comprise a total concentration of alcohol in an amount in therange of from about 0.001 to about 200 weight percent, in the range offrom about 1 to about 100 weight percent, or in the range of from 5 to15 weight percent based on the entire weight of all other components inthe medium formed in dissolution zone 20.

The medium formed in dissolution zone 20 can optionally comprise one ormore co-solvents. In one embodiment, the co-solvent employed can bemiscible or soluble with the medium formed in dissolution zone 20.Furthermore, in one embodiment the co-solvent does not act as a catalystfor esterification of cellulose, including the esterification processesdescribed in greater detail below. The medium formed in dissolution zone20 can comprise a total concentration of co-solvents in the range offrom about 0.01 to about 25 weight percent, in the range of from about0.05 to about 15 weight percent, or in the range of from 0.1 to 5 weightpercent based on the total concentration of ionic liquid in the mediumformed in dissolution zone 20. In one embodiment, the co-solvent cancomprise one or more carboxylic acids. Examples of suitable carboxylicacids useful in this embodiment include, but are not limited to, aceticacid, propionic acid, butyric acid, isobutyric acid, valeric acid,hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid,palmitic acid, stearic acid, benzoic acid, substituted benzoic acids,phthalic acid, and isophthalic acid. In one embodiment, the carboxylicacid in the medium formed in dissolution zone 20 can comprise aceticacid, propionic acid, and/or butyric acid.

In another embodiment, the co-solvent employed can comprise one or moreanhydrides. When one or more anhydrides are employed as co-solvents inthe medium formed in dissolution zone 20, the total amount of co-solventpresent can be in the range of from about 0.01 to about 20 molarequivalents, in the range of from about 0.5 to about 10 molarequivalents, or in the range of from 1.8 to about 4 molar equivalentsbased on the total amount of cellulose in the medium in dissolution zone20.

As is described in more detail below with reference to FIG. 2, at leasta portion of the carboxylic acids present in the medium formed indissolution zone 20 can originate from a recycled carboxylated ionicliquid introduced via line 70. Though not wishing to be bound by theory,the inventors have unexpectedly found that the presence of one or morecarboxylic acids in the medium in dissolution zone 20 appears to reducethe melting points of the ionic liquids employed, thereby allowingprocessing of the ionic liquids at lower temperatures than predicted.Additionally, it appears that the use of carboxylic acid in the mediumformed in dissolution zone 20 can reduce the viscosity of thecellulose-ionic liquid solution, thereby enabling easier processing ofthe solution. While the use of a co-solvent can reduce the viscosity ofthe cellulose-ionic liquid solution, the viscosity of thecellulose-ionic liquid solution can still vary significantly dependingon a number of factors, such as the type of ionic liquid employed, theDP of the cellulose, the amount of cellulose in the solution, and theamount of co-solvent present in the solution. Table 1, below, providesviscosity ranges for several different cellulose-ionic liquid solutionsat 0.1 rad/sec and a temperature of about 25° C., where each solutionhas a cellulose concentration of about 5 weight percent and a co-solventconcentration ranging from about 0.01 to about 25 weight percent, butwhere each solution has various ionic liquid types and cellulose DPvalues.

TABLE 1 Viscosities of Co-solvent-containing Cellulose-Ionic LiquidSolutions Ionic Liquid Viscosity Type Cellulose DP (poise) [BMIm]Cl1,090 <60,000 [AMIm]Cl 1,090 <140,000 [BMIm]OAc 1,090 <7,000 [EMIm]OAc1,090 <3,000 [BMIm]Cl 335 <650 [AMIm]Cl 335 <1,200When the co-solvent present in the cellulose-ionic liquid solution is ananhydride (as mentioned above), the viscosity can be lowered to asimilar degree. Thus, by way of illustration, cellulose-ionic liquidsolutions having an anhydride concentration in the range of from about0.01 to about 20 molar equivalents based on the total amount ofcellulose in the ionic liquid, and also having a cellulose concentrationof about 5 weight percent can have the same viscosity values as thosereported in Table 1, above, at 0.1 rad/sec and a temperature of about25° C.

In addition to the above, in one embodiment, a cellulose-ionic liquidsolution comprising in the range of from about 0.01 to about 25 weightpercent of a co-solvent can have a viscosity that is at least 1, atleast 5, at least 10, or at least 20 percent lower than the viscosity ofthe same cellulose-ionic liquid solution without any co-solvent.Additionally, when the co-solvent employed is an anhydride present inthe range of from about 0.01 to about 20 molar equivalents based on thetotal amount of cellulose in the ionic liquid, a co-solvent-containingcellulose-ionic liquid solution can have a viscosity that is at least 1,at least 5, at least 10, or at least 20 percent lower than the viscosityof the same cellulose-ionic liquid solution without any co-solvent.

In one embodiment, the medium formed in dissolution zone 20 canoptionally comprise one or more immiscible, substantially immiscible,insoluble, or sparingly soluble co-solvents. As used herein, the terms“substantially immiscible” and “sparingly soluble,” when used inconjunction with a co-solvent, shall denote a co-solvent capable offorming no more than a 1 weight percent solution with the chosen primarysolvent (e.g., a cellulose dissolving ionic liquid). Such co-solventscan comprise one or more components that are immiscible or sparinglysoluble with the cellulose-ionic liquid medium formed in dissolutionzone 20. Surprisingly, the addition of an immiscible or sparinglysoluble co-solvent does not cause precipitation of the cellulose uponcontacting the medium formed in dissolution zone 20. However, uponcontact with an acylating reagent, as will be discussed in more detailbelow, the cellulose can be esterified, which can in turn alter thesolubility of the now cellulose ester-ionic liquid solution with respectto the formerly immiscible or sparingly soluble co-solvent such that theco-solvent can be miscible or soluble with the esterified medium.Accordingly, subsequent to esterification, the contact mixture canbecome a single phase or highly dispersed mixture containing celluloseester, ionic liquid, and co-solvent.

The inventors have surprisingly discovered that the resulting singlephase or highly dispersed esterified medium appears to have a lowersolution viscosity than the initial cellulose-ionic liquid solution.This discovery is significant in that heretofore highly viscouscellulose solutions can now be used to make cellulose esters while stillmaintaining the ability to mix and process the solution. This discoveryalso provides a viable method to process highly viscous cellulose-ionicliquid solutions at lower contact temperatures. Accordingly, in oneembodiment, an esterified medium (such as the esterified medium in line80, described in more detail below) can have a viscosity that is atleast 1 percent, at least 5 percent, or at least 10 percent lower thanthe viscosity of the medium formed in dissolution zone 20.

Immiscible or sparingly soluble co-solvents suitable for use in thepresent invention can comprise alkyl or aryl esters, ketones, alkylhalides, hydrophobic ionic liquids, and the like. Specific examples ofimmiscible or sparingly soluble co-solvents include, but are not limitedto, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate,methyl butyrate, acetone, methyl ethyl ketone, chloroform, methylenechloride, alkyl imidazolium hexafluorophosphate, alkyl imidazoliumtriflimide, and the like. In one embodiment, the immiscible or sparinglysoluble co-solvents can comprise methyl acetate, methyl propionate,methyl butyrate, methyl ethyl ketone, and/or methylene chloride. Theweight ratio of immiscible or sparingly soluble co-solvents tocellulose-ionic liquid mixture can be in the range of from about 1:20 toabout 20:1, or in the range of from 1:5 to 5:1.

The medium formed in dissolution zone 20 can optionally comprise anacylating reagent, as is discussed in more detail below. The optionalacylating reagent can be introduced into dissolution zone 20 via line78. In one embodiment, the medium formed in dissolution zone 20 cancomprise acylating reagent in an amount in the range of from about 0.01to about 20 molar equivalents, in the range of from about 0.5 to about10 molar equivalents, or in the range of from 1.8 to about 4 molarequivalents based on the total amount of cellulose in the medium indissolution zone 20. As will be discussed in more detail below, incertain cases the amount of acylating reagent can be minimized inrelation to the amount of cellulose employed.

The medium formed in dissolution zone 20 can also comprise recycledionic liquid, as is discussed in more detail below with reference toFIG. 2. The recycled ionic liquid can be introduced into dissolutionzone 20 via line 70. The medium formed in dissolution zone 20 cancomprise recycled ionic liquid in an amount in the range of from about0.01 to about 99.99 weight percent, in the range of from about 10 toabout 99 weight percent, or in the range of from 90 to 98 weight percentbased on the total amount of ionic liquid in dissolution zone 20.

In one embodiment, the cellulose entering dissolution zone 20 via line62 can initially be dispersed in the ionic liquid. Dispersion of thecellulose in the ionic liquid can be achieved by any means known in theart. In one embodiment, dispersion of the cellulose can be achieved bymechanical mixing, such as mixing by one or more mechanicalhomogenizers.

After the cellulose has been dispersed in the ionic liquid, dissolutionof the cellulose in dissolution zone 20, along with removal of at leasta portion of any volatile components in the mixture, can be achievedusing any method known in the art. For example, dissolution of thecellulose can be achieved by lowering the pressure and/or raising thetemperature of the cellulose-ionic liquid dispersion initially formed indissolution zone 20. Accordingly, after the cellulose is dispersed inthe ionic liquid, the pressure can be lowered in dissolution zone 20. Inone embodiment, the pressure in dissolution zone 20 can be lowered toless than about 100 millimeters mercury (“mm Hg”), or less than 50 mmHg. Additionally, the cellulose-ionic liquid dispersion can be heated toa temperature in the range of from about 60 to about 100° C., or in therange of from 70 to 85° C.

After dissolution, the resulting solution can be maintained at theabove-described temperatures and pressures for a time in the range offrom about 0 to about 100 hours, or in the range of from 1 to 4 hours.The cellulose solution formed in dissolution zone 20 can comprisedissolved cellulose in an amount of at least 10 weight percent based onthe entire weight of the solution. In another embodiment, the cellulosesolution formed in dissolution zone 20 can comprise cellulose in anamount in the range of from about 1 to about 40 weight percent, or inthe range of from 5 to 20 weight percent, based on the entire weight ofthe solution.

Following dissolution, at least a portion of the resulting cellulosesolution can be removed from dissolution zone 20 via line 66 and routedto esterification zone 40. While in esterification zone 40, at least aportion of the cellulose can undergo esterification. In one embodiment,at least one acylating reagent can be employed to aid in esterifying atleast a portion of the cellulose. The acylating can be introduced atvarious points in the process depicted in FIG. 1. In one embodiment, theacylating reagent can be introduced into esterification zone 40 to aidin esterification of the cellulose. Additionally, as mentioned above,the acylating reagent can be introduced into dissolution zone 20.Furthermore, the acylating reagent can be added after the cellulose hasbeen dissolved in the ionic liquid. Optionally, at least a portion ofthe acylating reagent can be added to the ionic liquid prior todissolution of the cellulose in the ionic liquid. Regardless of where orwhen the acylating reagent is added, at least a portion of the cellulosein esterification zone 40 can undergo esterification subsequent to beingcontacted with the acylating reagent.

As used herein, the term “acylating reagent” shall denote any chemicalcompound capable of donating at least one acyl group to a cellulose. Asused herein, the term “acyl group” shall denote any organic radicalderived from an organic acid by the removal of a hydroxyl group.Acylating reagents useful in the present invention can be one or more C₁to C₂₀ straight- or branched-chain alkyl or aryl carboxylic anhydrides,carboxylic acid halides, diketene, or acetoacetic acid esters. Examplesof carboxylic anhydrides suitable for use as acylating reagents in thepresent invention include, but are not limited to, acetic anhydride,propionic anhydride, butyric anhydride, isobutyric anhydride, valericanhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoicanhydride, lauric anhydride, palmitic anhydride, stearic anhydride,benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride,and isophthalic anhydride. Examples of carboxylic acid halides suitablefor use as acylating reagents in the present invention include, but arenot limited to, acetyl, propionyl, butyryl, hexanoyl, 2-ethylhexanoyl,lauroyl, palmitoyl, and stearoyl chlorides. Examples of acetoacetic acidesters suitable for use as acylating reagents in the present inventioninclude, but are not limited to, methyl acetoacetate, ethylacetoacetate, propyl acetoacetate, butyl acetoacetate, and tert-butylacetoacetate. In one embodiment, the acylating reagents can be C₂ to C₉straight- or branched-chain alkyl carboxylic anhydrides selected fromthe group consisting of acetic anhydride, propionic anhydride, butyricanhydride, 2-ethylhexanoic anhydride, and nonanoic anhydride.

Referring still to FIG. 1, the reaction medium formed in esterificationzone 40 can comprise cellulose in an amount in the range of from about 1to about 40 weight percent, in the range of from about 5 to about 25weight percent, or in the range of from 10 to 20 weight percent, basedon the weight of the ionic liquid in the reaction medium. Additionally,the reaction medium formed in esterification zone 40 can comprise ionicliquid in an amount in the range of from about 20 to about 98 weightpercent, in the range of from about 30 to about 95 weight percent, or inthe range of from 50 to 90 weight percent based on the total weight ofthe reaction medium. Furthermore, the reaction medium formed inesterification zone 40 can comprise acylating reagent in an amount inthe range of from about 1 to about 50 weight percent, in the range offrom about 5 to about 30 weight percent, or in the range of from 10 to20 weight percent based on the total weight of the reaction medium.Furthermore, the reaction medium formed in esterification zone 40 canhave a cumulative concentration of nitrogen containing bases andcarboxylic acids in an amount less than 15 weight percent, less than 5weight percent, or less than 2 weight percent. Moreover, the reactionmedium formed in esterification zone 40 can comprise any of theabove-mentioned co-solvents (i.e., miscible and/or immiscibleco-solvents) in an amount in the range of from about 0.01 to about 40weight percent, in the range of from about 0.05 to about 20 weightpercent, or in the range of from 0.1 to 5 weight percent based on thetotal weight of the reaction medium. In another embodiment, the reactionmedium formed in esterification zone 40 can comprise carboxylic acids ina combined amount in the range of from about 0.01 to about 25 weightpercent, in the range of from about 0.05 to about 15 weight percent, orin the range of from about 0.1 to 5 weight percent based on the weightof the ionic liquid in the reaction medium.

In one embodiment, the weight ratio of cellulose-to-acylating reagent inesterification zone 40 can be in the range of from about 9:1 to about1:9, in the range of from about 3:2 to about 1:3, or in the range offrom 9:11 to 7:13. In one embodiment, the acylating reagent can bepresent in esterification zone 40 in an amount less than 5, less than 4,less than 3, or less than 2.7 molar equivalents per anhydroglucose unitin the cellulose.

In one embodiment of the present invention, when a halide ionic liquidis employed as the cellulose dissolving ionic liquid, a limited excessof acylating reagent can be employed during esterification of thecellulose to achieve a cellulose ester with a particular DS. Thus, inone embodiment, less than 20 percent molar excess, less than 10 percentmolar excess, less than 5 percent molar excess, or less than 1 percentmolar excess of acylating reagent can be employed during esterification.

Optionally, one or more catalysts can be introduced into esterificationzone 40 to aid in esterification of the cellulose. The catalyst employedin the present invention can be any catalyst that increases the rate ofesterification in esterification zone 40. When a catalyst is employed inesterification zone 40, the catalyst can be added to the cellulosesolution prior to adding the acylating reagent, which is discussed ingreater detail below. In another embodiment the catalyst can be added tothe cellulose solution as a mixture with the acylating reagent.

In one embodiment, the catalyst employed in the present invention can bean acidic component. In one embodiment, the acidic component employed inesterification zone 40 can comprise one or more protic acids. As usedherein, the term “protic acid” shall denote any acid capable of donatingat least one proton. Protic acids suitable for use in the presentinvention can have a pK_(a) value in the range of from about −5 to about10, or in the range of from −2.5 to 2.0. Protic acids suitable for usein the present invention can include sulfuric acid, alkyl sulfonicacids, and aryl sulfonic acids. Specific examples of protic acidssuitable for use in the present invention include, but are not limitedto, methane sulfonic acid (“MSA”), p-toluene sulfonic acid, and thelike.

In another embodiment, the acidic component employed in esterificationzone 40 can be one or more Lewis acids. Lewis acids suitable for use asthe acidic component in esterification zone 40 can be of the typeMX_(n), where M is a transition metal exemplified by B, Al, Fe, Ga, Sb,Sn, As, Zn, Mg, or Hg, and X is halogen, carboxylate, sulfonate,alkoxide, alkyl, or aryl. Examples of Lewis acids suitable for use ascatalysts include, but are not limited to, ZnCl₂, Zn(OAc)₂, and thelike.

Additionally, functional ionic liquids can be employed as catalystsduring esterification of the cellulose. Functional ionic liquids areionic liquids containing specific functional groups, such as hydrogensulfonate, alkyl or aryl sulfonates, and carboxylates, that effectivelycatalyze the esterification of cellulose using an acylating reagent.Examples of functional ionic liquids include 1-alkyl-3-methylimidazoliumhydrogen sulfate, methyl sulfonate, tosylate, and trifluoroacetate,where the alkyl can be a C₁ to C₁₀ straight-chain alkyl group.Additionally, suitable functional ionic liquids for use in the presentinvention are those in which the functional group is covalently linkedto the cation.

An example of a covalently-linked functional ionic liquid suitable foruse in the present invention includes, but is not limited to, thefollowing structure:

where at least one of the R₁, R₂, R₃, R₄, R₅ groups are replaced withthe group (CHX)_(n)Y, where X is hydrogen or halide, n is an integer inthe range of from 1 to 10, and Y is sulfonic or carboxylate, and theremainder R₁, R₂, R₃, R₄, R₅ groups are those previously described inrelation to the cations suitable for use as the cellulose dissolvingionic liquid. Examples of covalently-linked functional ionic liquidssuitable for use in the present invention include, but are not limitedto, 1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluorobutyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium,1-alkyl-3-(1-sulfonylethyl)imidazolium,1-alkyl-3-(1-sulfonylpropyl)imidazolium,1-alkyl-3-(1-sulfonylbutyl)imidazolium, and1-alkyl-3-(1-sulfonylhexyl)imidazolium, where the alkyl can be a C₁ toC₁₀ straight-chain alkyl group.

The amount of catalyst used to catalyze the esterification of cellulosemay vary depending upon the type of catalyst employed, the type ofacylating reagent employed, the type of ionic liquid, the contacttemperature, and the contact time. Thus, a broad concentration ofcatalyst employed is contemplated by the present invention. In oneembodiment, the amount of catalyst employed in esterification zone 40can be in the range of from about 0.01 to about 30 mol percent catalystper anhydroglucose unit (“AGU”), in the range of from about 0.05 toabout 10 mol percent catalyst per AGU, or in the range of from 0.1 to 5mol percent catalyst per AGU. In one embodiment, the amount of catalystemployed can be less than 30 mol percent catalyst per AGU, less than 10mol percent catalyst per AGU, less than 5 mol percent catalyst per AGU,or less than 1 mol percent catalyst per AGU.

The inventors have discovered a number of surprising and unpredictableadvantages apparently associated with employing a catalyst as a binarycomponent (e.g., acidic component, functional ionic liquid) during theesterification of cellulose. For example, the inventors have discoveredthat the inclusion of a binary component can accelerate the rate ofesterification. Very surprisingly, the binary component can also serveto improve solution and product color, prevent gelation of theesterification mixture, provide increased DS values in relation to theamount of acylating reagent employed, and/or help to decrease themolecular weight of the cellulose ester product. In one embodiment, whena catalyst is employed as a binary component, the amount of binarycomponent employed can be in the range of from about 0.01 to about 100mol percent per AGU, in the range of from about 0.05 to about 20 molpercent per AGU, or in the range of from 0.1 to 5 mol percent per AGU.

In addition to the above, it has been discovered that the use of abinary component can lower the viscosity of the reaction medium inesterification zone 40. Accordingly, when the initial medium formed inesterification zone 40 comprises 1-butyl-3-methylimidazolium chloride asthe ionic liquid, one or more binary components in a total amount in therange of from about 0.01 to about 100 mol percent per AGU, and cellulosehaving a DP of about 1,090 in an amount of at least 5 weight percent,the medium can have a viscosity of less than about 60,000 poise at 0.1rad/sec at a temperature of about 25° C. Furthermore, when the initialmedium formed in esterification zone 40 comprises1-allyl-3-methylimidazolium chloride as the ionic liquid, one or morebinary components in a total amount in the range of from about 0.01 toabout 100 mol percent per AGU, and cellulose having a DP of about 1,090in an amount of at least 5 weight percent, the medium can have aviscosity of less than about 140,000 poise at 0.1 rad/sec at atemperature of about 25° C. Additionally, when the medium formed inesterification zone 40 comprises 1-butyl-3-methylimidazolium chloride asthe ionic liquid, one or more binary components in an amount in therange of from about 0.01 to about 100 mol percent per AGU, and cellulosehaving a DP of about 335 in an amount of at least 5 weight percent, themedium can have a viscosity of less than about 650 poise at 0.1 rad/secat a temperature of about 25° C. Moreover, when the medium formed inesterification zone 40 comprises 1-allyl-3-methylimidazolium chloride asthe ionic liquid, one or more binary components in an amount in therange of from about 0.01 to about 100 mol percent per AGU, and cellulosehaving a DP of about 335 in an amount of at least 5 weight percent, themedium can have a viscosity of less than about 650 poise at 0.1 rad/secat a temperature of about 25° C.

It should be noted that binary components suitable to be employed in thepresent invention are not limited to catalysts such as acidic componentsor functional ionic liquids. Rather, as used herein, the term “binarycomponent” shall denote any non-cellulosic substance that, upon additionto the ionic liquid, alters the network structure of the ionic liquid.By way of illustration, the structure of an exemplary ionic liquidnetwork appears as follows:

As can be seen from the above structure, an ionic liquid can comprise anetwork of ionically linked anions and cations. However, upon additionof a binary component this network may become disrupted. This change innetwork structure may lead to the observed surprising and unpredictedadvantages of using a binary component.

As mentioned above, at least a portion of the cellulose can undergo anesterification reaction in esterification zone 40. The esterificationreaction carried out in esterification zone 40 can operate to convert atleast a portion of the hydroxyl groups present on the cellulose to estergroups, thereby forming a cellulose ester. As used herein, the term“cellulose ester” shall denote a cellulose polymer having at least oneester substituent. In one embodiment, at least a portion of the estergroups on the resulting cellulose ester can originate from theabove-described acylating reagent. The cellulose esters thus preparedcan comprise the following structure:

where R₂, R₃, and R₆ can independently be hydrogen, so long as R₂, R₃,and R₆ are not all hydrogen simultaneously on every AGU, or C₁ to C₂₀straight- or branched-chain alkyl or aryl groups bound to the cellulosevia an ester linkage.

In one embodiment, when the ionic liquid employed is a carboxylatedionic liquid, one or more of the ester groups on the resulting celluloseester can originate from the ionic liquid in which the cellulose isdissolved. Additionally, the ester group(s) on the cellulose esteroriginating from the carboxylated ionic liquid can be a different estergroup than the ester group(s) on the cellulose ester that originatesfrom the acylating reagent. Though not wishing to be bound by theory, itis believed that when an acylating reagent is introduced into acarboxylated ionic liquid, an anion exchange can occur such that one ormore carboxylate anions originating from the acylating reagent replaceat least a portion of the carboxylate anions originally in thecarboxylated ionic liquid, thereby creating an altered ionic liquid,which is discussed in more detail below. When the carboxylate anionsoriginating from the acylating reagent are of a different type than thecarboxylate anions of the ionic liquid, then the altered ionic liquidcan comprise at least two different types of carboxylate anions. Thus,so long as the carboxylate anions from the carboxylated ionic liquidcomprise a different acyl group than is found on the acylating reagent,at least two different acyl groups are available for esterification ofthe cellulose. By way of illustration, if cellulose was dissolved in1-butyl-3-methylimidazolium acetate (“[BMIm]OAc” or “[BMIm]acetate”) anda propionic anhydride (“Pr₂O”) acylating reagent was added to thecarboxylated ionic liquid, the carboxylated ionic liquid can become analtered ionic liquid, comprising a mixture of [BMIm]acetate and[BMIm]propionate. Thus, the process of forming a cellulose ester underthese conditions can be illustrated as follows:

As illustrated, contacting a solution of cellulose dissolved in[BMIm]acetate with a propionic anhydride can result in the formation ofa cellulose ester comprising both acetate ester substituents andpropionate ester substituents. Thus, as mentioned above, at least aportion of the ester groups on the cellulose ester can originate fromthe ionic liquid, and at least a portion of the ester groups canoriginate from the acylating reagent. When this scenario occurs, theamount of ester groups on the resulting cellulose ester that originatefrom the carboxylated ionic liquid can be at least 10 percent, at least25 percent, at least 50 percent, or at least 75 percent of the totalnumber of ester groups on the resulting cellulose ester. Additionally,at least one of the ester groups donated by the ionic liquid can be anacyl group. In one embodiment, all of the ester groups donated by theionic liquid can be acyl groups.

Therefore, in one embodiment, the cellulose ester prepared by methods ofthe present invention can be a mixed cellulose ester. As used herein,the term “mixed cellulose ester” shall denote a cellulose ester havingat least two different ester substituents on a single cellulose esterpolymer chain. The mixed cellulose ester of the present invention cancomprise a plurality of first pendant acyl groups and a plurality ofsecond pendant acyl groups, where the first pendant acyl groupsoriginate from the ionic liquid, and the second pendant acyl groupsoriginate from the acylating reagent. In one embodiment, the mixedcellulose ester can comprise a molar ratio of at least two differentpendant acyl groups in the range of from about 1:10 to about 10:1, inthe range of from about 2:8 to about 8:2, or in the range of from 3:7 to7:3. Additionally, the first and second pendant acyl groups canindividually comprise acetyl, propionyl, butyryl, isobutyryl, valeryl,hexanoyl, 2-ethylhexanoyl, nonanoyl, lauroyl, palmitoyl, benzoyl,substituted benzoyl, phthalyl, isophthalyl, and/or stearoyl groups. Inone embodiment, the first and second pendant acyl groups individuallycomprise acetyl, propionyl, and/or butyryl groups.

In one embodiment, at least one of the first pendant acyl groups can bedonated by the ionic liquid or at least one of the second pendant acylgroups can be donated by the ionic liquid. As used herein, the term“donated,” with respect to esterification, shall denote a directtransfer of an acyl group. Comparatively, the term “originated,” withrespect to esterification, can signify either a direct transfer or anindirect transfer of an acyl group. In one embodiment of the invention,at least 50 percent of the above-mentioned first pendant acyl groups canbe donated by the ionic liquid, or at least 50 percent of the secondpendant acyl groups can be donated by the ionic liquid. Furthermore, atleast 10 percent, at least 25 percent, at least 50 percent, or at least75 percent of all of the pendant acyl groups on the resulting celluloseester can result from donation of acyl groups by the ionic liquid.

In one embodiment, the above-described mixed cellulose ester can beformed by a process where a first portion of the first pendant acylgroups can initially be donated from the acylating reagent to thecarboxylated ionic liquid, and then the same acyl groups can be donatedfrom the carboxylated ionic liquid to the cellulose (i.e., indirectlytransferred from the acylating reagent to the cellulose, via the ionicliquid). Additionally, a second portion of the first pendant acyl groupscan be donated directly from the acylating reagent to the cellulose.

Referring again to FIG. 1, the temperature in esterification zone 40during the above-described esterification process can be in the range offrom about 0 to about 120° C., in the range of from about 20 to about80° C., or in the range of from 25 to 50° C. Additionally, the cellulosecan have a residence time in esterification zone 40 in the range of fromabout 1 minute to about 48 hours, in the range of from about 30 minutesto about 24 hours, or in the range of from 1 to 5 hours.

Following the above-described esterification process, an esterifiedmedium can be withdrawn from esterification zone 40 via line 80. Theesterified medium withdrawn from esterification zone 40 can comprise aninitial cellulose ester. In one embodiment, the initial cellulose esterin line 80 can be a non-random cellulose ester. As used herein, the term“non-random cellulose ester” shall denote a cellulose ester having anon-Gaussian distribution of substituted monomers as determined by NMRspectroscopy. Additionally, the initial cellulose ester in line 80 canbe a mixed cellulose ester, as described above.

The initial cellulose ester can have a degree of substitution (“DS”) inthe range of from about 0.1 to about 3.0, in the range of from about 1.8to about 2.9, or in the range of from 2.0 to 2.6. In another embodiment,the initial cellulose ester can have a DS of at least 2. In yet anotherembodiment, the initial cellulose ester can have a DS of less than 3.0,or less than 2.9.

In another embodiment, when a binary component is employed inesterification zone 40, at least 50, at least 60, or at least 70 percentof the ester substituents on the initial cellulose ester can comprisealkyl esters having a carbon chain length at least 6 carbon atoms long,at least 7 carbon atoms long, or at least 8 carbon atoms long.Additionally, the average ester substituent chain length of the initialcellulose ester can be at least 6 carbon atoms long, at least 7 carbonatoms long, or at least 8 carbon atoms long. In this embodiment, theinitial cellulose ester can have a DS of at least 1.5, at least 1.7, orat least 2.0.

As mentioned above, in another embodiment a limited excess of acylatingreagent can be employed during esterification in esterification zone 40.For example, a molar excess of less than 20 percent, less than 10percent, less than 5 percent, or less than 1 percent of acylatingreagent can be employed during esterification. In this embodiment, theresulting initial cellulose ester can have a DS of at least 1.8, or atleast 2.0.

The degree of polymerization (“DP”) of the cellulose esters prepared bythe methods of the present invention can be at least 10, at least 50, atleast 100, or at least 250. In another embodiment, the DP of the initialcellulose ester can be in the range of from about 5 to about 1,000, orin the range of from 10 to 250.

In addition to the initial cellulose ester, the esterified medium inline 80 can comprise altered ionic liquid, residual acylating reagent,one or more carboxylic acids, and/or residual binary component. As usedherein and as is discussed in more detail below, the term “altered ionicliquid” refers to an ionic liquid that has previously passed through acellulose esterification step wherein at least a portion of the ionicliquid acted as an acyl group donor and/or recipient. The esterifiedmedium in line 80 can comprise the initial cellulose ester in an amountin the range of from about 2 to about 80 weight percent, in the range offrom about 10 to about 60 weight percent, or in the range of from 20 to40 weight percent based on the total weight of ionic liquid in theesterified medium. In one embodiment, the esterified medium in line 80can comprise altered ionic liquid in an amount in the range of fromabout 0.01 to about 99.99 weight percent, in the range of from about 10to about 99 weight percent, or in the range of from 90 to 98 weightpercent relative to the amount of initial ionic liquid introduced intodissolution zone 20. Additionally, the esterified medium in line 80 cancomprise residual acylating reagent in an amount less than about 20weight percent, less than about 10 weight percent, or less than 5 weightpercent.

Furthermore, the esterified medium in line 80 can comprise a totalconcentration of carboxylic acids in an amount in the range of fromabout 0.01 to about 40 weight percent, in the range of from about 0.05to about 20 weight percent, or in the range of from 0.1 to 5 weightpercent. In another embodiment, the esterified medium in line 80 cancomprise a total concentration of carboxylic acids in an amount lessthan 40, less than 20, or less than 5 weight percent. Carboxylic acidsthat can be present in the esterified medium in line 80 include, but arenot limited to, formic acid, acetic acid, propionic acid, butyric acid,isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid,nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid,substituted benzoic acids, phthalic acid, and/or isophthalic acid.

In one embodiment of the present invention, the esterified medium inline 80 can be in the form of a solution. In this embodiment, theesterified solution in line 80 can comprise a total concentration of theabove-described co-solvents in an amount in the range of from about 0.01to about 40 weight percent, in the range of from about 0.05 to about 20weight percent, or in the range of from about 0.1 to 5 weight percent.

Following esterification, the esterified medium in line 80 can be routedto cellulose ester recovery/treatment zone 50. As is discussed in moredetail below with reference to FIG. 2, at least a portion of the initialcellulose ester from the esterified medium can optionally be subjectedto at least one randomization process in recovery/treatment zone 50,thereby producing a randomized cellulose ester. Additionally, as isdiscussed in more detail below with reference to FIG. 2, at least aportion of the cellulose ester from the esterified medium can be causedto precipitate out of the esterified medium, at least a portion of whichcan thereafter be separated from the resulting mother liquor.Furthermore, the separated cellulose ester can then optionally bewashed, as is described in more detail below with reference to FIG. 2.

Referring still to FIG. 1, at least a portion of the cellulose esterprecipitated and recovered in recovery/treatment zone 50 can bewithdrawn via line 90 as a final cellulose ester. The final celluloseester exiting recovery/treatment zone 50 via line 90 can have a numberaverage molecular weight (“Mn”) in the range of from about 1,200 toabout 200,000, in the range of from about 6,000 to about 100,000, or inthe range of from 10,000 to 75,000. Additionally, the final celluloseester exiting recovery/treatment zone 50 via line 90 can have a weightaverage molecular weight (“Mw”) in the range of from about 2,500 toabout 420,000, in the range of from about 10,000 to about 200,000, or inthe range of from 20,000 to 150,000. Furthermore, the final celluloseester exiting recovery/treatment zone 50 via line 90 can have aZ-average molecular weight (“Mz”) in the range of from about 4,000 toabout 850,000, in the range of from about 12,000 to about 420,000, or inthe range of from 40,000 to 330,000. The final cellulose ester exitingrecovery/treatment zone 50 via line 90 can have a polydispersity in therange of from about 1.3 to about 7, in the range of from about 1.5 toabout 5, or in the range of from 1.8 to 3. Additionally, the finalcellulose ester in line 90 can have a DP and DS as described above inrelation to the initial cellulose ester in line 80. Furthermore, thecellulose ester can be random or non-random, as is discussed in moredetail below with reference to FIG. 2. Moreover, the final celluloseester in line 90 can comprise a plurality of ester substituents asdescribed above. Also, the final cellulose ester in line 90 canoptionally be a mixed cellulose ester as described above.

In one embodiment, the cellulose ester in line 90 can be in the form ofa wet cake. The wet cake in line 90 can comprise a total liquid contentof less than 99, less than 50, or less than 25 weight percent.Furthermore, the wet cake in line 90 can comprise a total ionic liquidconcentration of less than 1, less than 0.01, or less than 0.0001 weightpercent. Additionally, the wet cake in line 90 can comprise a totalalcohol content of less than 100, less than 50, or less than 25 weightpercent. Optionally, as is discussed in greater detail below withreference to FIG. 2, the final cellulose ester can be dried to produce adry final cellulose ester product.

The cellulose esters prepared by the methods of this invention can beused in a variety of applications. Those skilled in the art willunderstand that the specific application in which the cellulose ester isused will depend upon various characteristics of the cellulose ester,such as, for example, the type of acyl substituent, DS, DP, molecularweight, and type of cellulose ester copolymer. In one embodiment of thepresent invention, the cellulose esters can be used in thermoplasticapplications in which the cellulose ester is used to make film or moldedobjects. Examples of cellulose esters suitable for use in thermoplasticapplications include, but are not limited to, cellulose acetate,cellulose propionate, cellulose butyrate, cellulose acetate propionate,cellulose acetate butyrate, or mixtures thereof.

In another embodiment of the invention, the cellulose esters can be usedin coating applications. Examples of coating applications include but,are not limited to, automotive, wood, plastic, or metal coatingprocesses. Examples of cellulose esters suitable for use in coatingapplications include cellulose acetate, cellulose propionate, cellulosebutyrate, cellulose acetate propionate, cellulose acetate butyrate, ormixtures thereof.

In yet another embodiment of the invention, the cellulose esters can beused in personal care applications. In personal care applications,cellulose esters can be dissolved or suspended in appropriate solvents.The cellulose ester can then act as a structuring agent, delivery agent,and/or film forming agent when applied to skin or hair. Examples ofcellulose esters suitable for use in personal care applications include,but are not limited to, cellulose acetate, cellulose propionate,cellulose butyrate, cellulose acetate propionate, cellulose acetatebutyrate, cellulose hexanoate, cellulose 2-ethylhexanoate, celluloselaurate, cellulose palmitate, cellulose stearate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters canbe used in drug delivery applications. In drug delivery applications,the cellulose ester can act as a film former, such as in the coating oftablets or particles. The cellulose ester can also be used to formamorphous mixtures of poorly soluble drugs, thereby improving thesolubility and bioavailability of the drugs. The cellulose esters canalso be used in controlled drug delivery, where the drug can be releasedfrom a cellulose ester matrix in response to external stimuli such as achange in pH. Examples of cellulose esters suitable for use in drugdelivery applications include, but are not limited to cellulose acetate,cellulose propionate, cellulose butyrate, cellulose acetate propionate,cellulose acetate butyrate, cellulose acetate phthalate, or mixturesthereof.

In a further embodiment of the invention, the cellulose esters of thepresent invention can be used in applications involving solvent castingof film. Examples of such applications include photographic film andprotective film for liquid crystalline displays. Examples of celluloseesters suitable for use in solvent cast film applications include, butare not limited to, cellulose triacetate, cellulose acetate, cellulosepropionate, and cellulose acetate propionate.

Referring still to FIG. 1, at least a portion of the mother liquorseparated in cellulose ester recovery/treatment zone 50 can be withdrawnvia line 86 and routed to ionic liquid recovery/treatment zone 60 as arecycle stream. As will be discussed in further detail below withreference to FIG. 2, the recycle stream can undergo various treatmentsin ionic liquid recovery/treatment zone 60. Such treatment can include,but is not limited to, volatiles removal and reformation of the ionicliquid. Reformation of the ionic liquid can include, but is not limitedto, (1) anion homogenization, and (2) anion exchange. Accordingly, arecycled ionic liquid can be formed in ionic liquid recovery/treatmentzone 60.

In the embodiment depicted in FIG. 1, at least a portion of the recycledionic liquid formed in ionic liquid recovery/treatment zone 60 can bewithdrawn via line 70. The recycled ionic liquid in line 70 can havesubstantially the same composition as the ionic liquid described abovewith reference to line 64 of FIG. 1. The production and composition ofthe recycled ionic liquid will be discussed in greater detail below withreference to FIG. 2. As mentioned above, at least a portion of therecycled ionic liquid in line 70 can be routed back to dissolution zone20. In one embodiment, at least about 80 weight percent, at least about90 weight percent, or at least 95 weight percent of the recycled ionicliquid produced in ionic liquid recovery/treatment zone 60 can be routedto dissolution zone 20.

Referring now to FIG. 2, a more detailed diagram for the production ofcellulose esters is depicted, including optional steps for improving theoverall efficacy and/or efficiency of the cellulose ester productionprocess. The process depicted in FIG. 2 includes such additional and/oroptional steps as cellulose modification, cellulose ester randomization,precipitation, washing, and drying.

In the embodiment depicted in FIG. 2, cellulose can be introduced intoan optional modification zone 110 via line 162. The cellulose fed tooptional modification zone 110 can be substantially the same as thecellulose in line 62 described above with reference to FIG. 1. Inoptional modification zone 110, the cellulose can be modified employingat least one modifying agent. The modifying agent suitable for use inthe present invention can be any substance capable of increasing thedispersibility of the cellulose in an ionic liquid.

In one embodiment, the modifying agent employed in modification zone 110can comprise water. Thus, following modification, a water-wet cellulosecan be withdrawn from optional modification zone 110 and added to one ormore ionic liquids in dissolution zone 120. In one embodiment, thecellulose can be mixed with water then pumped into one or more ionicliquids as a slurry. Alternatively, excess water can be removed from thecellulose, and thereafter the cellulose can be added to the one or moreionic liquids in the form of a wet cake. In one embodiment, thewater-wet cellulose introduced into dissolution zone 120 can comprisewater in an amount of at least 10 weight percent, at least 15 weightpercent, or at least 20 weight percent based on the combined weight ofthe cellulose and water. In another embodiment, the cellulose wet cakeintroduced into dissolution zone 120 can contain water in an amount inthe range of from about 10 to about 95 weight percent, in the range offrom about 20 to about 80 weight percent, or in the range of from 25 to75 weight percent, based on the combined weight of the cellulose andwater. It should be noted that the type of water employed as a modifyingagent is not critical, and can include tap, deionized, and/or purifiedwater.

Though not wishing to be bound by theory, the use of an initiallywater-wet cellulose in the production of cellulose esters hasunexpectedly and unpredictably been found to provide at least threeheretofore unknown benefits. First, water appears to increase dispersionof the cellulose in ionic liquids so that when removal of water isinitiated while heating the cellulose, the cellulose dissolves morequickly. Second, the presence of water appears to reduce the meltingpoints of ionic liquids, including those that are normally solids atroom temperature, thus allowing processing of ionic liquids at ambienttemperatures. A third benefit is that the molecular weight of celluloseesters prepared using initially water-wet cellulose is reduced duringthe above-described esterification process when compared to celluloseesters prepared using initially dry cellulose.

This third benefit is particularly surprising and useful. Under typicalcellulose ester processing conditions, the molecular weight of celluloseis not reduced during dissolution or during esterification. That is, themolecular weight of the cellulose ester product is directlyproportionate to the molecular weight of the initial cellulose. Typicalwood pulps used to prepare cellulose esters generally have a DP in therange of from about 1,000 to about 3,000. However, depending on theend-use application, the desired DP range of cellulose esters can be inthe range of from about 10 to about 500. Thus, in the absence ofmolecular weight reduction during esterification, the cellulose must bespecially treated either prior to dissolving the cellulose in the ionicliquid or after dissolving in the ionic liquid but prior toesterification. However, when employing water as at least one of theoptional modifying agents, pretreatment of the cellulose is not requiredsince molecular weight reduction can occur during esterification.Accordingly, in one embodiment of the present invention, the DP of themodified cellulose subjected to esterification can be within about 10percent of, within about 5 percent of, within 2 percent of, orsubstantially the same as the DP of the initial cellulose subjected tomodification, while the DP of the cellulose ester product can have a DPthat is less than about 90 percent, less than about 70 percent, or lessthan 50 percent of the DP of the modified cellulose subjected toesterification.

Referring still to FIG. 2, the optionally modified cellulose in line 166can be introduced into dissolution zone 120. Once in dissolution zone120, the optionally modified cellulose can be dispersed in one or moreionic liquids in substantially the same manner as described above withreference to dissolution zone 20 in FIG. 1. Subsequently, at least aportion of the modifying agent in the resulting cellulose-ionic liquidmixture can be removed. In one embodiment, at least 50 weight percent,at least 75 weight percent, at least 95 weight percent, or at least 99weight percent of all modifying agents can be removed from thecellulose-ionic liquid mixture. Removal of the one or more modifyingagents from dissolution zone 120 can be accomplished by any means knownin the art for liquid/liquid separation, such as, for example,distillation, flash vaporization, and the like. In one embodiment,removal of at least a portion of the one or more modifying agents can beaccomplished by lowering the pressure and/or raising the temperature ofthe cellulose-ionic liquid mixture. Removed modifying agent can bewithdrawn from dissolution zone 120 via line 124.

After removal of the modifying agent, dissolution zone 120 can produce acellulose solution in substantially the same manner as dissolution zone20, as described above with reference to FIG. 1. However, when amodifying agent is employed for modification of the initial cellulose,dissolution of the modified cellulose in dissolution zone 120 can becarried out for a dissolution period of less than 120 minutes, less than90 minutes, or less than 60 minutes, while at least 90, at least 95, orat least 99 weight percent of the modified cellulose dissolves duringthe dissolution period.

Following dissolution, a cellulose solution can be withdrawn fromdissolution zone 120 via line 176. The cellulose solution in line 176can comprise ionic liquid, cellulose, and a residual concentration ofone or more optional modifying agents. The cellulose solution in line176 can comprise cellulose in an amount in the range of from about 1 toabout 40 weight percent, in the range of from about 5 to about 30 weightpercent, or in the range of from 10 to 20 weight percent, based on theweight of the ionic liquid. Furthermore, the cellulose solution in line176 can comprise a cumulative amount of residual modifying agents in anamount of less than about 50 weight percent, less than about 25 weightpercent, less than about 15 weight percent, less than about 5 weightpercent, or less than 1 weight percent.

In the embodiment of FIG. 2, at least a portion of the cellulosesolution in line 176 can be introduced into esterification zone 140.Esterification zone 140 can be operated in substantially the same manneras esterification zone 40, as described above with reference to FIG. 1.For example, an acylating reagent can be introduced into esterificationzone 140 via line 178. As in esterification zone 40, the acylatingreagent can assist in esterifying at least a portion of the cellulose inesterification zone 140. Additionally, as described above, at least aportion of the resulting cellulose ester can comprise one or more estersubstituents that originated from and/or were donated by the ionicliquid.

After esterification in esterification zone 140, an esterified mediumcan be withdrawn via line 180. The esterified medium in line 180 can besubstantially the same as the esterified medium in line 80, as describedabove with reference to FIG. 1. Thus, the esterified medium in line 180can comprise an initial cellulose ester and other components, such as,for example, altered ionic liquid, residual acylating reagent, one ormore carboxylic acids, and/or one or more catalysts. The concentrationsof the initial cellulose ester and other components in the esterifiedmedium in line 180 can be substantially the same as the esterifiedmedium in line 80, as described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above the initial celluloseester produced in esterification zone 140 can be a non-random celluloseester. In one embodiment, at least a portion of the initial cellulose inline 180 can optionally be introduced into randomization zone 151 toundergo randomization, thereby creating a random cellulose ester.Randomization of the initial cellulose can comprise introducing at leastone randomizing agent into randomization zone 151 via line 181, therebyforming a randomization medium. Additionally, as will be discussed infurther detail below, at least a portion of the randomizing agentintroduced into randomization zone 151 can be introduced via line 194.

The randomizing agent employed in the present invention can be anysubstance capable lowering the DS of the cellulose ester via hydrolysisor alcoholysis, and/or capable of causing migration of at least aportion of the acyl groups on the cellulose ester from one hydroxyl to adifferent hydroxyl, thereby altering the initial monomer distribution.Examples of suitable randomizing agents include, but are not limited towater and/or alcohols. Alcohols suitable for use as the randomizingagent include, but are not limited to, methanol, ethanol, n-propanol,i-propanol, n-butanol, i-butanol, t-butanol, phenol and the like. In oneembodiment, methanol can be employed as the randomizing agent introducedinto randomization zone 151 via line 181.

The amount of randomizing agent introduced into randomization zone 151can be in the range of from about 0.5 to about 20 weight percent, or inthe range of from 3 to 10 weight percent, based on the total weight ofthe resulting randomization medium in randomization zone 151. Therandomization medium can have any residence time in randomization zone151 suitable to achieve the desired level of randomization of thecellulose ester. In one embodiment, the randomization medium can have aresidence time in randomization zone 151 in the range of from about 1min. to about 48 hours, in the range of from about 30 min. to about 24hours, or in the range of from 2 to 12 hours. Additionally, thetemperature in randomization zone 151 during randomization can be anytemperature suitable to achieve the desired level of randomization ofthe cellulose ester. In one embodiment, the temperature in randomizationzone 151 during randomization can be in the range of from about 20 toabout 120° C., in the range of from about 30 to about 100° C., or in therange of from 50 to 80° C.

Those skilled in the art will understand that the DS and DP of therandom cellulose ester might be less than that of the non-randomcellulose ester. Accordingly, in this embodiment the non-randomcellulose ester entering randomization zone 151 may optionally have agreater DS and/or DP than the target DS and/or DP of the randomcellulose ester.

In one embodiment of the present invention, it may be desirable toproduce cellulose esters that are at least partially soluble in acetone.Accordingly, the initial cellulose ester produced in esterification zone140 can bypass optional randomization zone 151, thereby producing afinal non-random cellulose ester. Non-random cellulose esters preparedby the methods of the present invention can be at least partiallysoluble in acetone when they have a DS in the range of from about 2.0 toabout 2.5, in the range of from about 2.1 to about 2.4, in the range offrom about 2.28 to about 2.39 or in the range of from 2.32 to 2.37.Additionally, cellulose esters prepared by the methods of the presentinvention can be sufficiently soluble in acetone to form an at least 1,at least 5, or at least 10 weight percent cellulose ester solution inacetone.

After optional randomization, an optionally randomized medium can bewithdrawn from randomization zone 151 via line 182. The optionallyrandomized medium can comprise a random cellulose ester and residualrandomizing agent. In one embodiment, the optionally randomized mediumin line 182 can comprise random cellulose ester in an amount in therange of from about 2 to about 80 weight percent, in the range of fromabout 10 to about 60 weight percent, or in the range of from 20 to 40weight percent based on the total weight of the ionic liquid in therandomized medium. Additionally, the optionally randomized medium cancomprise residual randomizing agent in the range of from about 0.5 toabout 20 weight percent, or in the range of from 3 to 10 weight percent,based on the total weight of the resulting randomized medium. Theoptionally randomized medium in line 182 also can comprise othercomponents, such as those described above with reference to theesterified medium in line 180 and with reference to the esterifiedmedium in line 80 of FIG. 1. Such components include, but are notlimited to, altered ionic liquid, residual acylating reagent, one ormore carboxylic acids, and/or one or more catalysts.

Following optional randomization, at least a portion of the esterifiedand optionally randomized medium in line 182 can be introduced intoprecipitation zone 152. Precipitation zone 152 can operate to cause atleast a portion of the cellulose ester from the esterified andoptionally randomized medium to precipitate. Any methods known in theart suitable for precipitating a substance out of solution can beemployed in precipitation zone 152. In one embodiment, one or moreprecipitating agents can be introduced into precipitation zone 152 vialine 183, thereby causing at least a portion of the cellulose ester toprecipitate out of the esterified and optionally randomized medium.Furthermore, as will be discussed in more detail below, at least aportion of the precipitating agent can optionally be introduced intoprecipitation zone 152 via line 194. In one embodiment, theprecipitating agent can be a non-solvent for the cellulose ester.Examples of suitable non-solvents that can be employed as precipitatingagents include, but are not limited to, C₁ to C₈ alcohols, water, ormixtures thereof. In one embodiment, the precipitating agent introducedinto precipitation zone 152 can comprise methanol.

The amount of precipitating agent introduced into precipitation zone 152can be any amount sufficient to cause at least a portion of thecellulose ester to precipitate out of the esterified and optionallyrandomized medium. In one embodiment, the amount of precipitating agentintroduced into precipitation zone 152 can be at least about 4 volumes,at least 10 volumes, or at least 20 volumes, based on the total volumeof the medium entering precipitation zone 152. The resultingprecipitation medium can have any residence time in precipitation zone152 suitable to achieve the desired level of precipitation. In oneembodiment, the precipitation medium can have a residence time inprecipitation zone 152 in the range of from about 1 to about 300 min.,in the range of from about 10 to about 200 min., or in the range of from20 to 100 min. Additionally, the temperature in precipitation zone 152during precipitation can be any temperature suitable to achieve thedesired level of precipitation. In one embodiment, the temperature inprecipitation zone 152 during precipitation can be in the range of fromabout 0 to about 120° C., in the range of from about 20 to about 100°C., or in the range of from 25 to 50° C. The amount of cellulose esterprecipitated in precipitation zone 152 can be at least 50 weightpercent, at least 75 weight percent, or at least 95 weight percent, ofthe total amount of cellulose ester in precipitation zone 152.

After precipitation in precipitation zone 152, a cellulose ester slurrycomprising a final cellulose ester can be withdrawn via line 184. Thecellulose ester slurry in line 184 can have a solids content of lessthan about 50 weight percent, less than about 25 weight percent, or lessthan 1 weight percent.

At least a portion of the cellulose ester slurry in line 184 can beintroduced into separation zone 153. In separation zone 153, at least aportion of the liquid content of the cellulose ester slurry can beseparated from the solids portion. Any solid/liquid separation techniqueknown in the art for separating at least a portion of a liquid from aslurry can be used in separation zone 153. Examples of solid/liquidseparation techniques suitable for use in the present invention include,but are not limited to, centrifugation, filtration, and the like.Furthermore, separation zone 153 can have any temperature or pressuresuitable for solid/liquid separation. In one embodiment, the temperaturein separation zone 153 during separation can be in the range of fromabout 0 to about 120° C., in the range of from about 20 to about 100°C., or in the range of from 25 to 50° C. In one embodiment, at least 50weight percent, at least 70 weight percent, or at least 90 weightpercent of the liquid portion of the cellulose ester slurry can beremoved in separation zone 153.

After separation in separation zone 153, a cellulose ester wet cake canbe withdrawn from separation zone 153 via line 187. Additionally, aswill be discussed in greater detail below, at least a portion of theseparated liquids from separation zone 153 can be withdrawn via line 186as a recycle stream. The cellulose ester wet cake in line 187 can have atotal solids content of at least 1 weight percent, at least 50 weightpercent, or at least 75 weight percent. Furthermore, the cellulose esterwet cake in line 187 can comprise cellulose ester in an amount of atleast 70 weight percent, at least 80 weight percent, or at least 90weight percent.

Once removed from separation zone 153, at least a portion of thecellulose ester solids from the cellulose ester wet cake can be washedin wash zone 154. Any methods known in the art suitable for washing awet cake can be employed in wash zone 154. An exemplary washingtechnique suitable for use in the present invention includes, but is notlimited to, a counter-current wash comprising at least 2 stages. In oneembodiment, a wash liquid comprising a washing agent that is anon-solvent for cellulose ester can be introduced into wash zone 154 vialine 188 to wash at least a portion of the cellulose ester solids. Suchnon-solvent washing agents include, but are not limited to, a C₁ to C₈alcohol, water, or mixtures thereof. In one embodiment, the non-solventwashing agent can comprise methanol. In one embodiment, the wash liquidcan additionally comprise water. Furthermore, as will be described ingreater detail below, at least a portion of the wash liquid canoptionally be introduced into wash zone 154 via line 194.

In one embodiment, washing of the cellulose ester solids in wash zone154 can be performed in such a manner that at least a portion of anyundesired byproducts and/or color bodies are removed from the celluloseester solids. Byproducts and/or color bodies can be removed from thecellulose ester via the use of at least one bleaching agent in the washliquid introduced via line 188. As used herein, the term “bleachingagent” shall denote any substance capable of decreasing the ΔE value ofa cellulose ester, as defined below. When one or more bleaching agentsare employed in wash zone 154, the wash liquid can contain the one ormore bleaching agents in a total combined amount in the range of fromabout 0.001 to about 50 weight percent, or in the range of from 0.01 to5 weight percent based on the total weight of the wash liquid.

In another embodiment, either in the alternative to or in addition tobeing contacted with a bleaching agent in wash zone 154, the celluloseester can be contacted with a bleaching agent while still at leastpartially dissolved in ionic liquid (i.e., prior to being precipitatedin precipitation zone 152). In this embodiment, the amount of bleachingagent employed can be in the range of from about 0.001 to about 2 weightpercent, in the range of from about 0.002 to about 1 weight percent, orin the range of from 0.003 to 0.2 weight percent based on the entireweight of the cellulose ester-ionic liquid solution. Additionally,during contacting the bleaching agent employed in this embodiment can beintroduced in the form of a dispersion in methanol at a concentration inthe range of from about 0.00001 to about 50 weight percent, or in therange of from about 0.0001 to about 5 weight percent.

Examples of bleaching agents suitable for use in the present inventioninclude, but are not limited to, chlorites, such as sodium chlorite(NaClO₂); hypohalites, such as sodium hypochlorite (NaOCl), sodiumhypobromite (NaOBr), and the like; peroxides, such as hydrogen peroxideand the like; peracids, such as peracetic acid and the like;permanganates, such as potassium permanganate (KMnO₄) and the like;manganates; elemental metals, such as iron, manganese, copper, chromium,and the like; sodium sulfites, such as sodium sulfite (Na₂SO₃), sodiummetabisulfite (Na₂S₂O₅), sodium bisulfite (NaHSO₃), and the like;perborates, such as sodium perborate (NaBO₃.nH₂O where n=1 or 4);chlorine dioxide (ClO₂); oxygen; and ozone. In one embodiment, thebleaching agent employed in the present invention can be selected fromthe group consisting of hydrogen peroxide, NaOCl, NaClO₂, and Na₂SO₃. Inanother embodiment, the bleaching agent employed in the presentinvention can comprise KMnO₄.

The resulting washed and/or bleached cellulose ester can have an a*value in the range of from about −5 to about 5, in the range of fromabout −2 to about 2, or in the range of from −1 to 1. Furthermore, theresulting washed and/or bleached cellulose ester can have a b* value inthe range of from about −12 to about 12, in the range of from about −6to about 6, or in the range of from −2 to 2. Additionally, the resultingwashed and/or bleached cellulose ester can have an L* value of at leastabout 90, or at least 98. As used herein, the terms L*, a*, and b*respectively denote color values from black to white, red to green, andyellow to blue, and are determined according to the CIE 1976 color spaceas specified by the International Commission on Illumination.

In one embodiment, the resulting washed and/or bleached cellulose estercan have a ΔE value of less than 30, less than 15, or less than 5.Additionally, the washed and/or bleached cellulose ester can have a ΔEvalue that is at least 5, at least 10, or at least 20 percent lower thanthe ΔE value of the initial cellulose ester produced in esterificationzone 140. As used herein, the term “ΔE” shall denote the colordifference between a cellulose ester and the reference materialn-methylpyrrolidone (“NMP”). By way of illustration, color measurementsare taken for a sample of neat NMP followed by taking color measurementsof a solution of cellulose ester dissolved in NMP. The ΔE value of thecellulose ester is then determined according to the following equation:

ΔE=[(Δa*)²+(Δb*)²+(ΔL*)²]^(1/2)

where Δa*, Δb*, and ΔL* are respectively the differences in a*, b* andL* values between the neat NMP and the solution of cellulose esterdissolved in NMP.

After washing in wash zone 154, a washed cellulose ester product can bewithdrawn via line 189. The washed cellulose ester product in line 189can be in the form of a wet cake, and can comprise solids in an amountof at least 1, at least 50, or at least 75 weight percent. Additionally,the washed cellulose ester product in line 189 can comprise celluloseester in an amount of at least 1, at least 50, or at least 75 weightpercent.

The washed cellulose ester product in line 189 can optionally be driedin drying zone 155. Drying zone 155 can employ any drying method knownin the art to remove at least a portion of the liquid content of thewashed cellulose ester product. Examples of drying equipment suitablefor use in drying zone 155 include, but are not limited to, rotarydryers, screw-type dryers, paddle dryers, and/or jacketed dryers. In oneembodiment, drying in drying zone 155 can be sufficient to produce adried cellulose ester product comprising less than 5, less than 3, orless than 1 weight percent liquids.

After drying in drying zone 155, a final cellulose ester product can bewithdrawn via line 190. The final cellulose ester product in line 190can be substantially the same as the final cellulose ester product inline 90, as described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above at least a portion of theseparated liquids generated in separation zone 153 can be withdrawn vialine 186 as a recycle stream. The recycle stream in line 186 cancomprise altered ionic liquid, one or more carboxylic acids, residualmodifying agent, residual catalyst, residual acylating reagent, residualrandomizing agent, and/or residual precipitation agent. Additionally,the recycle stream in line 186 can comprise one or more of theabove-described co-solvents. As mentioned above, the term “altered ionicliquid” refers to an ionic liquid that has previously passed through acellulose esterification step wherein at least a portion of the ionicliquid acted as an acyl group donor and/or recipient. As used herein,the term “modified ionic liquid” refers to an ionic liquid that haspreviously been contacted with another compound in an upstream processstep. Therefore, altered ionic liquids are a subset of modified ionicliquids, where the upstream process step is cellulose esterification.

In one embodiment, the recycle stream in line 186 can comprise alteredionic liquid, one or more carboxylic acids, one or more alcohols, and/orwater. In one embodiment, the recycle stream in line 186 can comprisealtered ionic liquid in an amount in the range of from about 10 to about99.99 weight percent, in the range of from about 50 to about 99 weightpercent, or in the range of from 90 to 98 weight percent, based on thetotal weight of the recycle stream in line 186. In one embodiment, atleast 50, at least 70, or at least 90 weight percent of the ionic liquidin the recycle stream in line 186 can ultimately be recycled for use indissolving additional cellulose.

In one embodiment, the altered ionic liquid can comprise an ionic liquidhaving at least two different anions: primary anions and secondaryanions. At least a portion of the primary anions in the altered ionicliquid can originate from the initial ionic liquid introduced intodissolution zone 120 via line 164, as described above. Additionally, atleast a portion of the secondary anions in the altered ionic liquid canoriginate from the acylating reagent introduced into esterification zone140, as described above. In one embodiment, the altered ionic liquid cancomprise primary anions and secondary anions in a ratio in the range offrom about 100:1 to about 1:100, in the range of from about 1:10 toabout 10:1, or in the range of from 1:2 to 2:1. Additionally, thealtered ionic liquid can comprise a plurality of cations, such as thosedescribed above with reference to the initial ionic liquid in line 68 ofFIG. 1.

The recycle stream in line 186 can comprise a total amount of carboxylicacids in an amount in the range of from about 5 to about 60 weightpercent, in the range of from about 10 to about 40 weight percent, or inthe range of from 15 to 30 weight percent based on the total weight ofionic liquid in the recycle stream in line 186. Examples of suitablecarboxylic acids the recycle stream in line 186 can comprise include,but are not limited to, acetic acid, propionic acid, butyric acid,isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid,nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid,substituted benzoic acids, phthalic acid, and isophthalic acid. In oneembodiment, at least 50 weight percent, at least 70 weight percent, orat least 90 weight percent of the carboxylic acids in the recycle streamin line 186 are acetic, propionic, and/or butyric acids.

Furthermore, the recycle stream in line 186 can comprise a totalconcentration of alcohols and/or water in an amount of at least 75volume percent, at least 85 volume percent, or at least 95 volumepercent, based on the total volume of the recycle stream. Examples ofsuitable alcohols the recycle stream in line 186 can comprise include,but are not limited to, C₁ to C₈ straight- or branched-chain alcohols.In one embodiment, at least 50 weight percent, at least 70 weightpercent, or at least 90 weight percent of the alcohol in the recyclestream in line 186 can comprise methanol.

As depicted in FIG. 2, at least a portion of the recycle stream in line186 can be introduced into ionic liquid recovery/treatment zone 160.Ionic liquid recovery/treatment zone 160 can operate to segregate and/orreform at least a portion of the recycle stream from line 186. In oneembodiment, at least a portion of the recycle stream can undergo atleast one flash vaporization and/or distillation process to remove atleast a portion of the volatile components in the recycle stream. Atleast 40 weight percent, at least 75 weight percent, or at least 95weight percent of the volatile components in the recycle stream can beremoved via flash vaporization. The volatile components removed from therecycle stream can comprise one or more alcohols. In one embodiment, thevolatile components can comprise methanol. After vaporization, theresulting volatiles-depleted recycle stream can comprise a total amountof alcohols in the range of from about 0.1 to about 60 weight percent,in the range of from about 5 to about 55 weight percent, or in the rangeof from 15 to 50 weight percent.

In one embodiment, at least a portion of the carboxylic acids can beremoved from the recycle stream. At least 10, at least 40, or at least70 weight percent of the carboxylic acids present in said recycle streamcan be removed. In one embodiment, this can be accomplished by firstconverting at least a portion of the carboxylic acids to carboxylateesters. In this embodiment, at least a portion of the recycle stream canbe placed into a pressurized reactor where the recycle stream can betreated at a temperature, pressure, and time sufficient to convert theat least a portion of the carboxylic acid to alkyl esters (e.g., methylesters), by reacting the carboxylic acids with alcohol present in therecycle stream. During esterification of the carboxylic acids, thepressurized reactor can have a temperature in the range of from about100 to about 180° C., or in the range of from 130 to 160° C.Additionally, the pressure in the pressurized reactor duringesterification can be in the range of from about 10 to about 1,000pounds per square inch gauge (“psig”), or in the range of from 100 to300 psig. The recycle stream can have a residence time in thepressurized reactor in the range of from about 10 to about 1,000minutes, or in the range of from 120 to 600 minutes. Prior to theabove-described esterification, the alcohol and carboxylic acid can bepresent in the recycle stream in a molar ratio in the range of fromabout 1:1 to about 30:1, in the range of from about 3:1 to about 20:1,or in the range of from 5:1 to 10:1 alcohol-to-carboxylic acid. In oneembodiment, at least 5, at least 20, or at least 50 mole percent of thecarboxylic acids can be esterified during the above-describedesterification.

As mentioned above, at least a portion of the carboxylic acids can beacetic, propionic, and/or butyric acids. Additionally, as mentionedabove, the alcohol present in the recycle stream can be methanol.Accordingly, the above-described esterification process can operate toproduce methyl acetate, methyl propionate, and/or methyl butyrate.Subsequent to esterification, at least 10, at least 50, or at least 95weight percent of the resulting carboxylate esters can be removed fromthe recycle stream by any methods known in the art. As depicted in FIG.2, at least a portion of the carboxylate esters produced by the abovedescribed esterification can be routed to dissolution zone 120 and/oresterification zone 140 via line 196. Carboxylate esters introduced intodissolution zone 120 and/or esterification zone 140 can be employed asimmiscible co-solvents, as described above. In another embodiment, atleast a portion of the carboxylate esters can be converted to anhydridesvia carbon monoxide insertion.

In one embodiment of the present invention, at least a portion of thealtered ionic liquid present in the recycle stream can undergoreformation. Reformation of the altered ionic liquid can optionally beperformed substantially simultaneously with the above-describedesterification of the carboxylic acids in the recycle stream.Alternatively, reformation of the altered ionic liquid can be performedsubsequently to the esterification of carboxylic acids in the recyclestream. Reformation of the altered ionic liquid can comprise at leastone anion exchange process.

In one embodiment, reformation of the altered ionic liquid can comprisethe step of anion homogenization via anion exchange, such thatsubstantially all of the anions of the altered ionic liquid areconverted to the same type of anion. In this embodiment, at least aportion of the altered ionic liquid can be contacted with at least onealkyl formate to assist in the anion exchange. Alkyl formates suitablefor use in the present invention include, but are not limited to, methylformate, ethyl formate, propyl formate, isopropyl formate, butylformate, isobutyl formate, tert-butyl formate, hexyl formate, octylformate, and the like. In one embodiment, the alkyl formate can comprisemethyl formate. Additionally, reformation of the altered ionic liquidcan be performed in the presence of one or more alcohols. Alcoholssuitable for use in this embodiment of the invention include, but arenot limited to, alkyl or aryl alcohols such as methanol, ethanol,n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol and thelike. In one embodiment, the alcohol present during reformation cancomprise methanol.

The temperature during reformation of the altered ionic liquid can be inthe range of from about 100 to about 200° C., or in the range of from130 to 170° C. Additionally, the pressure during reformation of thealtered ionic liquid can be at least 700 kPa, or at least 1,025 kPa.Furthermore, the reaction time of the reformation of the altered ionicliquid can be in the range of from about 10 min. to about 24 hours, orin the range of from 3 to 18 hours.

As mentioned above, reformation of the altered ionic liquid can compriseanion homogenization. In one embodiment, the resulting reformed ionicliquid can have an at least 90, at least 95, or at least 99 percentuniform anion content. Additionally, the reformed ionic liquid cancomprise an alkyl amine formate. In one embodiment, the amine of thealkyl amine formate can be an imidazolium. Examples of alkyl amineformates suitable for use as the reformed ionic liquid include, but arenot limited to, 1-methyl-3-methylimidazolium formate,1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazoliumformate, 1-butyl-3-methylimidazolium formate,1-hexyl-3-methylimidazolium formate, and/or 1-octyl-3-methylimidazoliumformate.

Following reformation, at least a portion of the volatile components inthe reformed ionic liquid can optionally be removed via any methodsknown in the art for removing volatile components. Volatile componentsremoved from the reformed ionic liquid can include, for example,carboxylate esters, such as those formed via the above describedcarboxylic acid esterification process. Thereafter, at least a portionof the reformed ionic liquid can undergo at least one anion exchangeprocess to replace at least a portion of the anions of the reformedionic liquid thereby forming a carboxylated ionic liquid. In oneembodiment, the reformed ionic liquid can be contacted with at least onecarboxylate anion donor to at least partially effect the anion exchange.Carboxylate anion donors suitable for use in this embodiment include,but are not limited to, one or more carboxylic acids, anhydrides, oralkyl carboxylates. Additionally, the carboxylate anion donors cancomprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or arylcarboxylic acids, anhydrides, or methyl esters. Furthermore, thecarboxylate anion donor can be one or more C₂ to C₁₂ straight-chainalkyl carboxylic acids, anhydrides, or methyl esters. Moreover, thecarboxylate anion donor can be one or more C₂ to C₄ straight-chain alkylcarboxylic acids, anhydrides, or methyl esters. The resultingcarboxylated ionic liquid can comprise cations and anions substantiallythe same as those found in the carboxylated ionic liquid described abovewith reference to the carboxylated ionic liquid in line 64 of FIG. 1.

When contacting the reformed ionic liquid with one or more carboxylateanion donors, the contacting can be carried out in a contact mixturefurther comprising alcohol and/or water. In one embodiment, the alcoholand/or water can be present in the contact mixture in the range of fromabout 0.01 to about 20 molar equivalents per alkyl amine formate, or inthe range of from 1 to 10 molar equivalents per alkyl amine formate. Inone embodiment, methanol can be present in the contact mixture in therange of from 1 to 10 molar equivalents per alkyl amine formate.

Referring still to FIG. 2, in one embodiment, at least a portion of thecarboxylated ionic liquid produced in ionic liquid recovery/treatmentzone 160 can be part of a treated ionic liquid mixture furthercomprising at least one alcohol, one or more types of residualcarboxylic acids, and/or water. The one or more alcohols and/or residualcarboxylic acids found in the treated ionic liquid mixture can besubstantially the same as described above with reference to the recyclestream in line 186. Following the above-described reformation process,the treated ionic liquid mixture can be subjected to at least oneliquid/liquid separation process to remove at least a portion of the oneor more alcohols in the mixture, if present. Such separation process cancomprise any liquid/liquid separation process known in the art, such as,for example, flash vaporization and/or distillation. Additionally, thetreated ionic liquid mixture can be subjected to at least oneliquid/liquid separation process to remove at least a portion of thewater, if present. Such separation process can comprise anyliquid/liquid separation process known in the art, such as, for example,flash vaporization and/or distillation.

In one embodiment, at least 50, at least 70, or at least 85 weightpercent of the alcohols and/or water can be removed from the treatedionic liquid mixture thereby producing a recycled carboxylated ionicliquid. At least a portion of the alcohol separated from the treatedionic liquid mixture can optionally be removed from ionic liquidrecovery/treatment zone 160 via line 194. The one or more alcohols inline 194 can thereafter optionally be routed to various other pointsdepicted in FIG. 2. In one embodiment, at least 50, at least 70, or atleast 90 weight percent of the alcohols removed from the treated ionicliquid mixture can be routed to various other points in the processdepicted in FIG. 2. In one optional embodiment, at least a portion ofthe alcohols in line 194 can be routed to randomization zone 151 to beemployed as a randomizing agent. In another optional embodiment, atleast a portion of the alcohols in line 194 can be routed toprecipitation zone 152 to be employed as a precipitating agent. In yetanother optional embodiment, at least a portion of the alcohols in line194 can be routed to wash zone 154 to be employed as a wash liquid.

In one embodiment, at least a portion of the water separated from thetreated ionic liquid mixture can optionally be removed from ionic liquidrecovery/treatment zone 160 via line 192. Optionally, at least a portionof the water removed from ionic liquid recovery/treatment zone 160 canbe routed to modification zone 110 to be employed as a modifying agent,as described above. At least about 5, at least about 20, or at least 50weight percent of the water separated from the treated ionic liquidmixture can optionally be routed to modification zone 110. Additionally,at least a portion of the water in line 192 can optionally be routed toa waste water treatment process (not shown).

After alcohol and/or water removal, the above-mentioned recycledcarboxylated ionic liquid can comprise residual carboxylic acid in anamount in the range of from about 0.01 to about 25 weight percent, inthe range of from about 0.05 to about 15 weight percent, or in the rangeof from 0.1 to 5 weight percent based on the entire weight of therecycled carboxylated ionic liquid. Additionally, the recycledcarboxylated ionic liquid can comprise sulfur in an amount of less than200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw.Furthermore, the recycled carboxylated ionic liquid can comprise halidesin an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw,or less than 10 ppmw. Moreover, the carboxylated ionic liquid cancomprise transition metals in an amount less than 200 ppmw, less than100 ppmw, less than 50 ppmw, or less than 10 ppmw.

In one embodiment, at least a portion of the recycled carboxylated ionicliquid produced in ionic liquid recovery/treatment zone 160 canoptionally be routed to dissolution zone 120. At least 50 weightpercent, at least 70 weight percent, or at least 90 weight percent ofthe recycled carboxylated ionic liquid produced in ionic liquidrecovery/treatment zone 160 can be routed to dissolution zone 120.

In dissolution zone 120, the recycled carboxylated ionic liquid can beemployed either individually or combined with the carboxylated ionicliquid entering dissolution zone 120 via line 164 to thereby form theabove-described cellulose dissolving ionic liquid. In one embodiment,the recycled carboxylated ionic liquid can make up in the range of fromabout 10 to about 99.99 weight percent, in the range of from about 50 toabout 99 weight percent, or in the range of from 90 to 98 weight percentof the cellulose dissolving ionic liquid in dissolution zone 120.

As mentioned above, in an alternative embodiment of the presentinvention, the cellulose dissolving ionic liquid employed can be ahalide ionic liquid. When a halide ionic liquid is employed, the recyclestream in line 186 can have substantially the same composition as thatdescribed above, with the exception that a halide ionic liquid ispresent in place of the carboxylated ionic liquid. In this embodiment,removal of components such as volatiles (e.g., alcohols) and carboxylicacids can be performed in substantially the same manner as describedabove. The remaining halide ionic liquid can then be recycled todissolution zone 120 without further processing (i.e., without an anionhomogenization or anion exchange step). Concentrations of recycledhalide ionic liquid in dissolution zone 120 can be the same as describedabove with reference to the recycled carboxylated ionic liquid.

This invention can be further illustrated by the following examples ofembodiments thereof, although it will be understood that these examplesare included merely for purposes of illustration and are not intended tolimit the scope of the invention unless otherwise specificallyindicated.

EXAMPLES Materials and Methods Used in Examples

Commercial grades of ionic liquids employed in the following exampleswere manufactured by BASF (Ludwigshafen, Germany) and were obtainedthrough Fluka (a subsidiary of Sigma-Aldrich, St. Louis, Mo., USA).These ionic liquids were used either as received or after furtherpurification as described in the examples that follow. Experimentalionic liquids (e.g., alkyl imidazolium carboxylates) were employed inthe following examples, and were prepared as described in the examplesthat follow. Cellulose was obtained from Sigma-Aldrich (St. Louis, Mo.,USA). The degree of polymerization (“DP”) of the Aldrich cellulose,which was approximately 335, was determined via capillary viscometryusing copper ethylenediamine (Cuen) as the solvent. Prior to dissolutionin ionic liquids, the cellulose was typically dried for 14-18 hours at50° C. and a pressure of 5 mm Hg, except in cases where the cellulosewas modified with water prior to dissolution.

Several of the Examples below indicate color values for variouscellulose ester samples. All color measurements were made following thegeneral protocol of ASTM D1925. Samples for color measurements wereprepared by dissolving 1.7 g of cellulose ester in 41.1 g ofn-methylpyrrolidone (“NMP”). A HunterLab Color Quest XE calorimeter witha 20 mm pathlength cell operating in transmittance mode was used foreach of the measurements. The calorimeter was interfaced to a standardcomputer running EasyMatch QC Software (HunterLab). Color values (i.e.,L*, white to black; a*, + red to − green; and b*, + yellow to − blue)were obtained for neat NMP and for the cellulose ester/NMP solutions.The color difference (ΔE) between the solvent and each of the samplesolutions was then calculated in accordance with the definition for ΔEprovided above.

Viscosity measurements provided in the following Examples weredetermined using an AR2000 rheometer (TA Instruments, LTD) interfacedwith a computer running TA Instruments Advantage software. The 25 mmaluminum stage for the rheometer was enclosed in a plastic cover with anitrogen purge to ensure that the samples did not acquire moistureduring the measurements.

Example 1 Preparation of Cellulose Ester Comparative

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 61 g of 1-butyl-3-methylimidazolium chloride (“[BMIm]Cl”),which, prior to addition, had been melted at 90° C. and then stored in adesiccator where the [BMIm]Cl remained a liquid. While stirring rapidly,3.21 g of previously dried microcrystalline cellulose, having a DP ofabout 335, was added in small portions over a period of 3 minutes. Theslurry was stirred for 5 minutes and then placed under vacuum. Afterapproximately 3 hours and 25 minutes, most of the cellulose haddissolved except for a few small pieces and 1 large piece attached tothe probe. After 5.5 hours, the oil bath temperature was increased to105° C. to speed up dissolution of the remaining cellulose. The solutionwas maintained at 105° C. for 1.5 hours (47 minute heat up) beforeallowing the solution to cool to room temperature and stand overnight atambient temperature.

After standing overnight, the cellulose-[BMIm]Cl solution was clear andthe IR spectra indicated that all of the cellulose was dissolved. Afterheating the solution to 80° C., 10.11 g (5 equivalents) of aceticanhydride (“Ac₂O”) was added dropwise over a period of 26 minutes. Thereaction was sampled throughout the reaction period by removing 6 to 10g aliquots of the reaction mixture and precipitating in 100 mL ofmethanol (“MeOH”). The solid from each aliquot was washed twice with 100mL portions of MeOH then twice with 100 mL of MeOH containing 8 weightpercent of 35% H₂O₂ before drying at 60° C. and 5 mm Hg. The firstsample was white, the second sample was tan, and the third sample wasbrown. During the course of the reaction, the solution becameprogressively darker. Approximately 2 hours and 45 minutes after thestart of the Ac₂O addition, the viscosity of the reaction mixtureabruptly increased, and then the reaction mixture completely gelled. Theoil bath was lowered and the contact solution was allowed to cool toroom temperature.

FIG. 3 is a plot of absorbance versus time for Example 1 and it showsthe dissolution of cellulose (1,046 cm⁻¹) and the removal of residualwater (1,635 cm⁻¹) from the mixture during the course of thedissolution. The spikes in the cellulose trend line are due to largecellulose gel particles, which are removed by the stirring action,sticking to the IR probe. Clumping occurs because the surfaces of thecellulose particles become partially dissolved before dispersion isobtained, which can lead to clumping and large gel particles. The dip inthe trend lines near the 6 hour mark is a result of the temperatureincrease from 80 to 105° C. This figure illustrates that approximately 6hours is required to fully dissolve the cellulose when the cellulose isadded to the ionic liquid that is preheated to 80° C.

FIG. 4 is a plot of absorbance versus time for Example 1 and itillustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), theconsumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid(1,706 cm⁻¹) during the experiment. The degree of substitution (“DS”)values shown in FIG. 4 were determined by NMR spectroscopy andcorrespond to the samples removed during the course of the contactperiod. As illustrated, approximately 75% of the acetylation occurredduring the first hour, after which the reaction rates slowed.Approximately 2 hours and 45 minutes from beginning the Ac₂O addition(DS=2.45), the solution viscosity suddenly increased followed bygelation of the contact mixture. At this point, no further reactionoccurred and the remaining contact solution was processed as describedabove. It should be noted that there was still a large excess of Ac₂O atthe point of gelation. Furthermore, during the course of the contactperiod, the solution became progressively darker and the final productcolor was dark brown. Color measurements of the final sample dissolvedin NMP gave an L* value of 82.74, an a* value of 2.23, a b* value of56.94, and an ΔE value of 59.55. In addition to determining the DS ofeach sample, the molecular weight of each sample was determined by gelpermeation chromatography (“GPC”) (reproduced in Table 2, below). Ingeneral, the weight average molecular weight (“Mw”) was approximately55,000 and the polydispersity ranged from 3-4. Based on the DP of thestarting cellulose, this analysis indicates that the molecular weight ofthe cellulose polymer remained essentially intact during the contactperiod.

Example 2 Modification of Cellulose with Water

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 64.3 g of [BMIm]Cl, which, prior to addition, had been meltedat 90° C. and then stored in a desiccator where the [BMIm]Cl remained aliquid. While stirring rapidly, 3.4 g (5 weight percent) ofmicrocrystalline cellulose, having a DP of about 335, was added atambient temperature. Approximately 12 minutes after adding thecellulose, the flask was placed in a preheated 80° C. oil bath. Afterabout 17 minutes in the 80° C. oil bath, upon visual inspection all ofthe cellulose appeared to be dissolved. A vacuum was applied afterapproximately 22 minutes in the 80° C. oil bath. To insure completeremoval of water, 50 minutes after applying vacuum, the oil bath settingwas increased to 105° C. and the solution was stirred for 2 hours and 25minutes before the oil bath was allowed to cool to room temperature.

The temperature of the clear, amber cellulose solution was adjusted to80° C. before adding 6.42 g of Ac₂O (3 eq.) dropwise over a period of 5minutes. The contact mixture was sampled throughout the reaction periodby removing 6 to 10 g aliquots of the contact mixture and precipitatingin 100 mL of MeOH. The solid from each aliquot was washed once with 100mL of MeOH then twice with MeOH containing 8 weight percent of 35% H₂O₂.The samples were then dried at 60° C. at a pressure of 5 mm Hgovernight. During the course of the contact period the color of thesolution became darker, ultimately becoming dark brown. Approximately 2hours and 10 minutes from the start of Ac₂O addition, the solutionviscosity began to increase significantly; 10 minutes later the solutioncompletely gelled and started climbing the stir shaft. The experimentwas aborted and MeOH was added to the flask to precipitate the remainingproduct.

The precipitation and the wash liquids from each aliquot were combinedand concentrated in vacuo at 68° C. until the vacuum dropped to 24 mmHg, which provided 54.2 g of recovered [BMIm]Cl. Analysis by ¹H NMRrevealed that the ionic liquid contained 4.8 weight percent acetic acidwhen measured by this technique.

FIG. 5 is a plot of absorbance versus time for Example 2, and it showsthe dissolution of cellulose (1,046 cm⁻¹) and the removal of residualwater (1,635 cm⁻¹) from the mixture during the course of thedissolution. As can be seen in FIG. 5, the dissolution of the cellulosewas very rapid (17 minutes, compared to 360 minutes in Example 1). Thiswas due to adding the cellulose to the ionic liquid at room temperature,stirring to get a good dispersion (higher surface area), then heating toeffect dissolution. Normally, [BMIm]Cl is a solid at room temperature,and melts at approximately 70° C. However, if water or a carboxylic acidis allowed to mix with [BMIm]Cl, the [BMIm]Cl will remain a liquid atroom temperature, thus allowing introduction of the cellulose at ambienttemperature. As can be seen from the water loss in FIG. 5, the [BMIm]Clcontained a significant amount water. This example illustrates that theaddition of water to an ionic liquid followed by cellulose addition andgood mixing to get a good dispersion allows for rapid dissolution ofcellulose.

FIG. 6 is a plot of absorbance versus time for Example 2, and itillustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), theconsumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid(1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 6 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Relative to Example 1, thereaction rate was slower (Example 1 indicates a DS of 2.44 at 165minutes, whereas Example 2 indicates a DS of only 2.01 at 166 minutes;compare Table 2, below). Similar to what was observed in Example 1, thesolution viscosity suddenly increased followed by gelation of thecontact mixture, but in Example 2, gelation occurred at a lower DS. Boththe slower reaction rate and gelation at a lower temperature can beattributed to the use of less Ac₂O. However, it should be noted thatthere was still a large excess of Ac₂O at the point of gelation. As withExample 1, during the course of the contact period, the solution becameprogressively darker and the final product color was dark brown. Colormeasurements of the final sample dissolved in NMP gave an L* value of67.30, an a* value of 17.53, a b* value of 73.35, and a ΔE value of82.22. In addition to determining the DS of each sample, the molecularweight of each sample was determined by GPC (Table 2, below). Ingeneral, Mw was approximately 55,000 and the polydispersity ranged from3-6. Based on the DP of the starting cellulose, this analysis indicatesthat the molecular weight of the cellulose polymer remained essentiallyintact during the contact period.

Example 3 MSA Secondary Component, No Modification with Water

3.58 g of cellulose (5 weight percent) was dissolved in 68 g of [BMIm]Clin a manner similar to Example 2. At a temperature of 80° C., a mixtureof 433 mg (0.2 eq.) of methane sulfonic acid (“MSA”) and 6.76 g of Ac₂O(3 eq.) was added to the cellulose solution dropwise over a period of 8minutes. The reaction was sampled throughout the reaction period byremoving 6 to 10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed twice with 100 mLportions of MeOH then dried at 60° C. at a pressure of 5 mm Hg. Thesolid samples were snow white. After approximately 2 hours, all of theAc₂O appeared to be consumed, according to the IR spectrum. Theexperiment was aborted and the remaining sample was processed as above.

The precipitation and the wash liquids from each aliquot were combinedand concentrated in vacuo at 68° C. until the vacuum dropped to 24 mmHg, which provided 64 g of recovered [BMIm]Cl. Unlike Example 2,analysis by ¹H NMR revealed that the ionic liquid did not contain anyacetic acid when measured by this technique. This result indicates thatMSA aids in the removal of residual acetic acid from the ionic liquid,probably by conversion of the residual acetic acid to methyl acetate.

FIG. 7 is a plot of absorbance versus time for Example 3, and itillustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), theconsumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid(1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 7 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. What is apparent from FIG. 7 isthat the rates of reaction are much faster compared to Examples 2 and 3.For example, 55 minutes were required to reach a DS of 1.82 in Example1-1 (Table 2, below) while only 10 minutes were required to reach a DSof 1.81 in Example 3-1. Similarly, 166 minutes were required to reach aDS of 2.01 in Example 2-4 (Table 2, below) while only 20 minutes wererequired to reach a DS of 2.18 in Example 3-2. Additionally, FIG. 7shows that no gelation occurred during the course of the experiment. Infact, throughout the experiment, there was no increase in solutionviscosity, the solution color was essentially unchanged from the initialsolution color, and the products isolated from the contact mixture wereall white. Color measurements of the final sample dissolved in NMP gavean L* value of 97.65, an a* value of −2.24, a b* value of 11.07, and aΔE value of 11.54. Comparison of these values to those obtained inExamples 1 and 2 (ΔE=59.55 and 82.22, respectively) shows that inclusionof a secondary component such as MSA in the contact mixturesignificantly improves solution and product color. This effect isparticularly pronounced in view of the fact that the samples in Examples1 and 2 were bleached and the samples in this Example were not bleached.As discussed in Example 36, below, bleaching can significantly improveproduct color for cellulose esters prepared from cellulose dissolved inionic liquids. Finally, it should be noted in Table 2, below, that theMw (ca. 40,000) for the samples of Example 3 are less than those forExamples 1 and 2, and that the polydispersity (Mw/Mn) is lower and morenarrow (2-3) than those for Examples 1 and 2 (3-6). When compared toExamples 1 and 2, Example 3 shows that inclusion of a secondarycomponent, such as MSA, in the contact mixture accelerates the rates ofreaction, significantly improves solution and product color, preventsgelation of the contact mixture, allows the achievement of high DSvalues while using less acylating reagent, and helps to promote loweringof the cellulose ester molecular weight.

TABLE 2 Properties of Cellulose Acetates Prepared in Examples 1 through3 Example Time (min) DS Mw Mw/Mn 1-1 55 1.82 59243 3.29 1-2 122 2.2561948 4.34 1-3 165 2.44 51623 3.73 2-1 6 0.64 50225 2.93 2-2 34 1.4956719 3.48 2-3 56 1.73 64553 5.4 2-4 166 2.01 66985 5.7 2-5 176 2.0563783 5.83 3-1 10 1.81 41778 1.92 3-2 20 2.18 43372 2.01 3-3 27 2.3941039 2.22 3-4 43 2.52 41483 2.4 3-5 66 2.62 40412 2.54 3-6 124 2.7239521 2.55

Example 4 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 58.07 g of [BMIm]Cl, which, prior to addition, had been meltedat 90° C. and then stored in a desiccator. The flask was placed in anoil bath and heated to 80° C.

3.06 g of water was added to 3.06 g (5 weight percent) ofmicrocrystalline cellulose having a DP of approximately 335. The slurrywas hand mixed and allowed to stand for approximately 30 minutes beforeadding the slurry in small portions to the [BMIm]Cl over a period of 5minutes. This gave a hazy solution in which the cellulose wassurprisingly well dispersed. The slurry was stirred for 27 minutes andthen placed under vacuum. After 28 minutes under vacuum, it appearedupon visual inspection that all of the cellulose had dissolved.Dissolution of the cellulose was confirmed by IR. According to the IRanalysis, there was still approximately 3 weight percent water in the[BMIm]Cl after all of the cellulose was dissolved. The system wasmaintained under vacuum at 80° C. to remove the remaining water. Thesample was then allowed to cool to room temperature and left standinguntil the next step.

After heating the cellulose solution to 80° C., a mixture of 5.78 g Ac₂O(3 eq.) and 368 mg MSA (0.2 eq.) was added dropwise over a period of 8minutes. The reaction was sampled throughout the reaction period byremoving 6 to 10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed twice with 100 mLportions of MeOH then dried at 60° C. at a pressure of 5 mm Hg. Theisolated samples were all white. The solution color was excellentthroughout the experiment and there was no indication of a viscosityincrease. After approximately 2 hours and 25 minutes, infraredspectroscopy indicated that all of the Ac₂O was consumed. The experimentwas aborted and the remaining sample was processed as above.

FIG. 8 is a plot of absorbance versus time for Example 4, and it showsthe dissolution of cellulose (1,046 cm⁻¹) and the removal of residualwater (1,635 cm⁻¹) from the mixture during the course of thedissolution. As can be seen, the dissolution of the water-wet(activated) cellulose was very rapid (28 minutes) despite the presenceof a significant amount of water. This is surprising in view of theconventional teachings. The addition of water-wet cellulose to the ionicliquid enables one to obtain a good dispersion of cellulose with littleclumping. Upon application of a vacuum to remove the water, thecellulose rapidly dissolves without clumping to form large particles.

FIG. 9 is a plot of absorbance versus time for Example 4, and itillustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), theconsumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid(1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 9 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Relative to Example 3, thereaction rate to produce cellulose acetate was similar. However, theweight average molecular weights of the cellulose acetate prepared inExample 4 (approximately 33,000; see Table 3, below) were notably lowerthan those observed in Example 3 and much lower than those observed inExamples 1 and 2 (see Table 2, above). Additionally, thepolydispersities for the samples of Example 4 are all less than 2, whichare less than those observed for the samples produced in Examples 1, 2,and 3.

This example illustrates that water-wet cellulose leads to goodcellulose dispersion in the ionic liquid and rapid cellulosedissolution. The reaction rate for formation of cellulose acetate israpid. Surprisingly, the use of water-wet cellulose leads to lowermolecular weight cellulose acetate with low polydispersities relative tothe use of dry cellulose. Additionally, the cellulose acetate made fromwater-wet cellulose has better acetone solubility relative to when drycellulose is utilized.

Example 5 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 67.33 g of [BMIm]Cl, which, prior to addition, had been meltedat 90° C. and then stored in a desiccator. The flask was placed in anoil bath and heated to 80° C. 7.08 g of water was added to 7.48 g (10weight percent) of microcrystalline cellulose, which had a DP ofapproximately 335. The cellulose slurry was hand mixed and allowed tostand for about 60 minutes before adding the slurry in small portions tothe [BMIm]Cl over a period of 8 minutes. This produced a hazy solutionin which the cellulose was surprisingly well dispersed. The slurry wasstirred for 10 minutes and then placed under vacuum. The cellulosedispersion was then stirred overnight.

Infrared spectroscopy indicated that essentially all of the cellulosewas dissolved within 50 minutes after applying vacuum; approximately 3.5hours were required to remove the water. A mixture of 14.13 g of Ac₂O (3eq.) and 884 mg (0.2 eq.) of MSA was added to the cellulose solutiondropwise over a period of 11 minutes. The reaction was sampledthroughout the reaction period by removing 6 to 10 g aliquots of thereaction mixture and precipitating in 100 mL of MeOH. The solid fromeach aliquot was washed twice with 100 mL portions of MeOH then dried at60° C. and a pressure of 5 mm Hg. The isolated samples were snow white.The solution color was excellent throughout the experiment and there wasno indication of a viscosity increase. After approximately 2 hours and10 minutes, infrared spectroscopy indicated that all of the Ac₂O wasconsumed. The experiment was aborted and the remaining sample wasprocessed as above.

FIG. 10 is a plot of absorbance versus time for Example 5 and it showsthe dissolution of cellulose (1,046 cm⁻¹) and the removal of residualwater (1,635 cm⁻¹) from the mixture during the course of thedissolution. As can be seen, the dissolution of the water-wet(activated) cellulose was very rapid (50 minutes) despite the presenceof a significant amount of water and the increase in celluloseconcentration relative to Example 4.

FIG. 11 is a plot of absorbance versus time for Example 5 and itillustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), theconsumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid(1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 11 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Despite the increase incellulose concentration, relative to Examples 3 and 4, the reaction rateto produce cellulose acetate in Example 5 was similar. The weightaverage molecular weights of the cellulose acetate prepared in Example 5(approximately 22,000; see Table 3, below) were notably lower than thoseobserved in Example 4 and much lower than those observed in Examples 1,2, and 3 (see Table 2, above). As was observed for Example 4, thepolydispersities for the samples of Example 5 are all less than 2, whichare less than those observed for the samples produced in Examples 1, 2,and 3.

This example illustrates that water-wet cellulose leads to goodcellulose dispersion in the ionic liquid and rapid cellulose dissolutioneven when the cellulose concentration is increased to 10 weight percent.The reaction rate for formation of cellulose acetate is rapid.Surprisingly, the use of water-wet cellulose at these concentrationsleads to even lower molecular weight cellulose acetates with lowpolydispersities relative to the use of dry cellulose. The celluloseacetate made from water-wet cellulose has better acetone solubilityrelative to when dry cellulose is utilized.

Example 6 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 51.82 g of [BMIm]Cl, which, prior to addition, had been meltedat 90° C. and then stored in a desiccator. The flask was placed in anoil bath and heated to 80° C. 53.6 g of water was added to 9.15 g (15weight percent) of microcrystalline cellulose, which had a DP ofapproximately 335. The cellulose slurry was hand mixed and allowed tostand in the water for 50 minutes before filtering, which produced 18.9g of a wet cellulose cake. The water-wet cellulose was then added insmall portions to the [BMIm]Cl over a period of 5 minutes. Within 2minutes, the cellulose was finely dispersed in the ionic liquid. Tenminutes after adding the cellulose to the [BMIm]Cl, the flask was placedunder vacuum. After about 1 hour, there were no visible celluloseparticles; the solution viscosity was very high and the solution startedclimbing the stir rod. The solution was left stirring overnight at 80°C. under vacuum.

Infrared spectroscopy indicated that about 1 hour was required forcellulose dissolution and 2 hours were required to strip the water tothe initial value. The cellulose solution was heated to 100° C.,followed by addition of a mixture of 17.28 g Ac₂O (3 eq.) and 1.087 g(0.2 eq.) of MSA, added dropwise over a period of 8 minutes. Thereaction was sampled throughout the reaction period by removing 6 to 10g aliquots of the reaction mixture and precipitating in 100 mL of MeOH.The solid from each aliquot was washed once with 100 mL of MeOH thentwice with MeOH containing 8 weight percent of 35% H₂O₂. The solidsamples were then dried at 60° C. at a pressure of 5 mm Hg. After about65 minutes, infrared spectroscopy indicated that all of the Ac₂O wasconsumed. The experiment was aborted and the remaining sample wasprocessed as above.

FIG. 12 is a plot of absorbance versus time for Example 6, and it showsthe dissolution of presoaked water-wet cellulose (1,046 cm⁻¹) and theremoval of residual water (1,635 cm⁻¹) from the mixture during thecourse of the dissolution. As can be seen, the dissolution of thewater-wet (activated) cellulose was very rapid (60 minutes), despite thepresence of a significant amount of water and the use of 15 weightpercent cellulose. Even more surprising was the rapid removal of water(about 2 hours) at this high cellulose concentration.

FIG. 13 is a plot of absorbance versus time for Example 6, and itillustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), theconsumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid(1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 13 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Despite the increase incellulose concentration (15 weight percent), acetic anhydride could beeasily mixed into the cellulose solution at 100° C. Again, the weightaverage molecular weights of the cellulose acetate prepared in Example 6(approximately 20,000; see Table 3, below) were notably lower than thoseobserved in Examples 1, 2, and 3 (approximately 39,000 to 67,000; seeTable 2, above) where the cellulose was dried prior to use. Also, thepolydispersities for the samples of Example 6 are all less than 2, whichare less than those observed for the samples produced in Examples 1, 2,and 3.

This example illustrates that water-wet cellulose leads to goodcellulose dispersion in the ionic liquid and rapid cellulose dissolutioneven when the cellulose concentration is increased to 15 weight percent.This example also shows that higher temperatures (e.g., 100° C.) canincrease reaction rates for formation of cellulose acetate.Surprisingly, the use of water-wet cellulose at these concentrationsleads to even lower molecular weight cellulose acetates with lowpolydispersities compared to the use of an initially dry cellulose.Furthermore, the cellulose acetate made from water-wet cellulose hasbetter acetone solubility relative to when initially dry cellulose isutilized.

TABLE 3 Effect of Water Modification on Properties of Cellulose AcetatesExample Time (min) DS Mw Mw/Mn 4-1 9 1.58 31732 1.73 4-2 13 1.94 335591.64 4-3 21 2.15 34933 1.63 4-4 35 2.28 31810 1.77 4-5 150 2.63 307711.89 5-1 11 1.95 24522 1.6 5-2 14 2.21 23250 1.67 5-3 18 2.35 22706 1.765-4 22 2.52 22692 1.79 5-5 31 2.59 21918 1.86 5-6 45 2.60 21628 1.89 5-770 2.66 19708 1.97 5-8 130 2.67 20717 1.99 6-1 10 2.63 20729 1.67 6-2 142.75 19456 1.78 6-3 18 2.80 19658 1.84 6-4 23 2.87 18966 1.84 6-5 322.89 20024 1.88 6-6 65 2.96 18962 1.85

Example 7 Miscible Co-Solvent

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 58.79 g of [BMIm]Cl, which, prior to addition, had been meltedat 90° C. and then stored in a desiccator. The flask was placed in anoil bath and heated to 80° C. After reaching 80° C., IR spectra datagathering was initiated before adding 1.82 g (3 weight percent) ofglacial acetic acid. The mixture was stirred for 12 minutes beforeadding 10.38 g (15 weight percent) cellulose (having a DP ofapproximately 335) as a water-wet cellulose cake (10.29 g water,prepared by soaking the cellulose for 50 minutes in excess water) over aperiod of 9 minutes. The mixture was then stirred for approximately 9minutes to allow the cellulose to disperse before applying a vacuum.After about 65 minutes, infrared spectroscopy indicated that all of thecellulose was dissolved (see FIG. 14). The solution was stirred for anadditional 70 minutes before adding 1.82 g of glacial acetic acid (6weight percent total). In order to reduce the solution viscosity, thestirring was turned off 8 minutes after adding the acetic acid and theoil bath temperature was increased to 100° C. After reaching 100° C.,stirring was resumed. Infrared spectroscopy indicated that upon resumedstirring, the acetic acid mixed well with the cellulose solution. Thefinal solution was clear and no cellulose particles were observed. Afterstanding for 10 days, the cellulose solution was still clear and couldbe hand stirred at room temperature.

This example shows that a significant amount of a miscible co-solventthat is compatible with cellulose acylation, such as a carboxylic acid(e.g., acetic acid), can be mixed with a cellulose-ionic liquid samplewhile still maintaining cellulose solubility. The use of such aco-solvent apparently has the unexpected benefit of reducing solutionviscosity, allowing for easier processing.

Example 8 Randomization

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 149.7 g of [BMIm]Cl. The flask was placed in an oil bath andheated to 80° C. 12.14 g of microcrystalline cellulose (7.5 weightpercent; having a DP of approximately 335) was added to 68.9 g of water.After hand mixing, the cellulose was allowed to stand in the water for45 minutes at 60° C. before filtering, which yielded 24.33 g of a wetcellulose cake. The water-wet cellulose was then added in small portionsto the [BMIm]Cl over a period of 5 minutes. Approximately 15 minutesafter adding the cellulose to the [BMIm]Cl, the flask was placed undervacuum by gradually lowering the vacuum, starting at about 120 mm Hg andending at about 1.4 mm Hg. After approximately 85 minutes, no visiblecellulose particles remained in the mixture and analysis by infraredspectroscopy indicated that all of the cellulose was dissolved. Thesolution was stirred overnight at 80° C. under vacuum.

After heating the cellulose solution to 80° C., a mixture of 22.93 gAc₂O (3 eq.) and 1.427 g (0.2 eq.) of MSA was added dropwise over aperiod of 15 minutes. The reaction was sampled throughout the reactionperiod by removing 6 to 10 g aliquots of the reaction mixture andprecipitating in 100 mL of MeOH. The solid from each aliquot was washedthree times with 100 mL portions of MeOH then dried at 60° C. at apressure of 5 mm Hg. After removing an aliquot 192 minutes after thestart of the Ac₂O addition, 1.21 g of MeOH was added to the contactmixture. The contact mixture was stirred for an additional 120 minutesbefore adding 1.95 g of water. The contact mixture was then stirredovernight at 80° C. (14 hours and 40 minutes) at which time, theexperiment was aborted and the remaining sample was processed as above.

The contact times, DS, and molecular weights for isolated samplesremoved from the contact mixture prepared above are summarized below inTable 4.

TABLE 4 Effect of Randomization on Cellulose Acetates Example Time (min)DS Mw Mw/Mn 8-1 16 1.95 26492 1.54 8-2 18 2.15 24838 1.57 8-3 21 2.2423973 1.63 8-4 25 2.33 23043 1.7 8-5 32 2.42 23499 1.79 8-6 57 2.5621736 1.82 8-7 190 2.73 20452 2.08 8-8 After MeOH Addition 2.73 204782.00 8-10 After H₂O Addition 2.59 21005 1.89

As indicated in Table 4, as contact time increased, the DS of thecellulose acetate increased (until water was added) and the Mwdecreased. Fifty-seven minutes after starting the contact period, thecellulose acetate sample had a DS of 2.56 and a Mw of 21,736. Prior toadding the MeOH/water, the DS was 2.73 and the Mw was 20,452. After thewater contact period, the isolated cellulose acetate had a DS of 2.59and a Mw of 21,005 indicating that the DS was reduced but the Mw wasunchanged.

FIG. 15 shows the proton NMR spectra of a cellulose acetate prepared bydirect acetylation (DS=2.56) and after randomization (DS=2.59). Both thering protons attached to the anhydroglucose monomers and acetyl protonsattached to the acetyl substituents are shown. FIG. 15 demonstrates thateven though these two cellulose acetates have essentially the same DS,they have a much different monomer content.

Example 9 MSA Secondary Component, Minimal Acylating Reagent

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 60.47 g of 1-allyl-3-methylimidazolium chloride (“[AMIm]Cl”).The flask was placed in an oil bath and heated to 80° C. 9.15 g ofmicrocrystalline cellulose (13 weight percent; having a DP ofapproximately 335) was added to 27.3 g of water. After hand mixing, thecellulose was allowed to stand in the water for 50 minutes at 60° C.before filtering, which yielded 9.44 g of a wet cellulose cake. Thewater-wet cellulose was then added in small portions to the [AMIm]Clover a period of 5 minutes. Approximately 15 minutes after adding thecellulose to the [AMIm]Cl, the flask was placed under vacuum bygradually lowering the pressure, starting at about 120 mm Hg. Afterapproximately 40 minutes, no visible cellulose particles remained in themixture and analysis by infrared spectroscopy indicated that all of thecellulose was dissolved. The solution was left stirring overnight at 80°C. under vacuum.

After heating the cellulose solution to 80° C., a mixture of 8.58 g Ac₂O(3 eq.) and 537 mg (0.2 eq.) of MSA was added dropwise over a period of5 minutes. The reaction was sampled throughout the reaction period byremoving 6 to 10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed three times with100 mL portions of MeOH and then dried at 60° C., 5 mm Hg. After all ofthe Ac₂O appeared to be consumed according to infrared spectroscopy, theexperiment was aborted and the remaining sample was processed as above.

The contact times, DS and molecular weights for isolated samples removedfrom the contact mixture prepared above are summarized below in Table 5.

TABLE 5 Contact Times and Properties of Cellulose Acetate Prepared in[AMIm]Cl. Example Time (min) DS Mw Mw/Mn 9-1 5 1.74 36192 1.69 9-2 82.24 35734 1.84 9-3 11 2.38 32913 1.9 9-4 15 2.48 31811 1.99 9-5 24 2.6031970 2.14 9-6 50 2.74 31302 2.36 9-7 109 2.82 30808 2.48

As indicated in Table 5, five minutes after starting the reaction thefirst cellulose acetate sample had a DS of 1.74 and a Mw of 36,192. Withincreasing contact time, the DS increased and the Mw decreased. After109 minutes, the DS was 2.82 and the Mw was 30,808. This example showsthat, compared to conventional methods, the method of Example 9 providesfor a higher DS and a significant reduction in cellulose acetatemolecular weight. By way of comparison, the conventional methoddescribed in Example 11, which is discussed in further detail below,requires 6.5 hours to yield a cellulose acetate with a DS of 2.42 and aMw of 50,839, while in Example 9, a cellulose acetate with a DS of 2.48and a Mw of 31,811 was achieved in only 15 minutes.

Example 10 Conventional Cellulose Ester Preparation (Comparative)

A solution of cellulose (5 weight percent) dissolved in 29.17 g of[BMIm]Cl was heated to 80° C. with an oil bath. The solution was heldunder vacuum (approximately 7 mm Hg) while stirring for 2 hours. To thecellulose solution was added 4.6 g (5 eq.) of Ac₂O over a period of 5minutes. During the course of the reaction, the solution color becamegradually darker (brown). After 2.5 hours, the solution had gelled, sothe contact solution was allowed to cool to room temperature. Theproduct was isolated by adding the solution to water then homogenizingto give a dispersed gel/powder. The mixture was filtered and washedextensively with water. After drying the solid in vacuo at 50° C., 2.04g of a pink powder was obtained that was insoluble in acetone. Analysisby ¹H NMR indicated that the sample had a DS of 2.52 and a Mw of 73,261.

Example 11 Conventional Cellulose Ester Preparation Comparative

33.8 g of [AMIm]Cl was added to a 3-neck 100 mL round bottom flaskequipped for mechanical stirring and having an N₂/vacuum inlet added.While stirring rapidly, 1.78 g of dry cellulose powder (5 weightpercent; having a DP of approximately 335) was added to the [AMIm]Cl.The flask was then placed under vacuum (2 mm Hg) and the mixture wasstirred at room temperature to insure that the cellulose was welldispersed. After 15 minutes, the cellulose was well dispersed and thesolution viscosity was rising. The flask was then placed in an oil bathwhich was heated to 80° C. After 40 minutes, all of the cellulose wasdissolved. The solution was maintained at 80° C. for 6.5 hours beforeallowing the solution to cool to room temperature and stand overnight.

The viscous solution was heated to 80° C. before adding 5.6 g (5 eq.) ofAc₂O dropwise over a period of 15 minutes. After 5 hours, the productwas isolated by pouring the mixture into 300 mL of MeOH. The MeOH/solidslurry was stirred for approximately 30 minutes before filtering toremove the liquids. The solid was then taken up in two 200 mL portionsof MeOH and the slurry was stirred for approximately 30 minutes beforefiltering to remove the liquids. The solids were dried overnight at 55°C. and a pressure of 6 mm Hg, yielding 2.27 g of a powder, which, whendissolved in acetone, gave a hazy acetone solution. Analysis by ¹H NMRand by GPC indicated that the sample had a DS of 2.42 and a Mw of50,839.

Example 12 MSA Secondary Component, Long Chain Aliphatic CelluloseEsters

A solution of cellulose (5 weight percent) dissolved in [BMIm]Cl washeated to 80° C. with an oil bath. The solution was held under vacuum(approximately 2.5 mm Hg) while stirring for 4 hours. A mixture of 10.88g (5 eq.) of nonanoic anhydride and 141 mg of MSA was added to thecellulose solution over a period of 25 minutes. After 18.5 hours, thesolution was allowed to cool to room temperature before it was pouredinto a solution of 80:20 MeOH:H₂O. After filtering, the solid was washedextensively with 85:15 MeOH:H₂O, followed by washing with 95:5 MeOH:H₂O.The sample was dried in vacuo which gave 3.7 g of a white powder solublein isododecane. Analysis by ¹H NMR indicated that the resulting productwas cellulose nonanoate having a DS of 2.49.

Achievement of a cellulose nonanoate with a high degree of substitutionby the method of this example is surprising in view of conventionalteachings that long chain aliphatic cellulose esters with a DS greaterthan about 1.5 cannot be prepared in ionic liquids.

Example 13 MSA Secondary Component, C₃ and C₄ Aliphatic Cellulose Esters

A solution of cellulose (5 weight percent) dissolved in [BMIm]Cl washeated to 80° C. with an oil bath. The solution was held under vacuum(approximately 6 mm Hg) while stirring overnight. A mixture of 7.91 g (5eq.) of butyric anhydride and 190 mg of MSA was added to the cellulosesolution over a period of 25 minutes. After 2.6 hours, the solution wasallowed to cool to room temperature before it was poured into water. Thesolid was washed extensively with water before drying in vacuo, whichyielded 2.62 g of a white powder soluble in acetone and 90:10CHCl₃:MeOH. Analysis by ¹H NMR indicated that the resulting product wascellulose butyrate having a DS of 2.59.

This example illustrates that C₃ and C₄ aliphatic cellulose estershaving high degrees of substitution can be prepared by the methods ofthis example.

Example 14 Homogenization of Cellulose Solution

193.6 g of solid [BMIm]Cl was added to a 1 L flat bottom kettle. A 3neck top was placed on the kettle and the kettle was fitted with anN₂/vacuum inlet and for mechanical stirring. The kettle was then placedin an 80° C. oil bath and the [BMIm]Cl was melted while stirring under avacuum of 6 mm Hg. After the [BMIm]Cl was completely melted, 10.2 g ofpreviously dried cellulose (having a DP of about 335) was added and themixture and was thereafter homogenized with a Heidolph Silent Crusher.After about 3 minutes of homogenization, essentially all of thecellulose was dissolved. The resulting solution was then stirred undervacuum (6 mm Hg) for an additional 1.5 hours, at which time all of thecellulose was dissolved.

This example illustrates that high intensity mixing can be used todisperse the cellulose which leads to rapid cellulose dissolution. Thisresult may be due to the increased surface area of the celluloseresulting from mixing.

Example 15 Acetone Solubility

The solubilities of cellulose acetate in acetone were evaluated asfollows: Acetone (Burdick & Jackson, high purity grade) was dried using4 A molecular sieves (purchased from Aldrich and stored in an oven at125° C.). All of the cellulose acetate samples were dried prior to usein a Eurotherm 91e vacuum oven (manufactured by Eurotherm Inc.,Leesburg, Va., USA) at 60° C. and a pressure of 5 mm Hg for at least 12hours. Each cellulose acetate sample was weighed into a 2 Dram vial (100mg±1 mg; obtained from VWR); thereafter, 1 mL±5 μL of dry acetone wasadded to each of the vials. The vials were then placed in an ultrasonicbath (VWR, model 75HT) and ultra-sonicated at room temperature for30-120 minutes, then removed and vortexed (VWR minivortexer) at roomtemperature using a speed setting of 10. If the cellulose acetateappeared to be dissolving but the rate of dissolution appeared to beslow, the vial was placed on a roller and mixed at approximately 15revolutions per minute overnight at ambient temperature. Following themixing period, the solubility of each cellulose acetate was rated asfollows:

Rating Description 1 Soluble, transparent with no visible particles 2Partially soluble, hazy 3 Partially soluble, very hazy, visibleparticles 4 Gel 5 Swollen solid 6 InsolubleCellulose acetates with a rating of 1 are very useful in allapplications in which acetone solubility or solubility in relatedsolvents (e.g., diethyl phthalate) is a critical factor (e.g., solventspinning of acetate fiber or melt processing of plasticized celluloseacetate). Cellulose acetates with a rating of 2 or 3 would requireadditional filtration to remove insoluble particles and/or the use ofco-solvents before they would have utility. Cellulose acetates with arating of 4-6 would not have utility in these applications. Hence,cellulose acetates with a rating of 1 are highly desired.

In Table 6, the solubility in acetone of cellulose acetates prepared inExamples 3-6, 8, and 9 are compared to the solubilities of the celluloseacetates prepared in Examples 1 and 2, and to the cellulose acetatesprepared by traditional methods (i.e., Examples 15-1 to 15-6). Thecellulose acetates prepared by traditional methods were prepared byacetylation of cellulose to make cellulose triacetate followed by H₂SO₄catalyzed reduction of DS, a process know to yield cellulose acetatesthat are random copolymers. In the absence of water (dry acetone), theacetone solubility of these cellulose acetates is known to be limited toa narrow range (from about 2.48 to about 2.52).

TABLE 6 Solubility of Cellulose Acetate in Acetone (100 mg/mL). ExampleDS Solubility 1-1 1.82 5 1-2 2.25 4 1-3 2.44 4 2-1 0.64 5 2-2 1.49 5 2-31.73 5 2-4 2.01 5 2-5 2.05 5 3-1 1.81 5 3-2 2.18 1 3-3 2.39 1 3-4 2.52 23-5 2.62 3 3-6 2.72 3 4-1 1.58 6 4-2 1.94 2 4-3 2.15 1 4-4 2.28 1 4-52.63 2 5-1 1.95 2 5-2 2.21 1 5-3 2.35 1 5-4 2.52 2 5-5 2.59 2 5-6 2.60 25-7 2.66 3 5-8 2.67 3 6-1 2.63 2 6-2 2.75 3 6-3 2.80 3 6-4 2.87 3 6-52.89 3 6-6 2.96 3 8-1 1.95 3 8-2 2.15 1 8-3 2.24 1 8-4 2.33 1 8-5 2.42 18-6 2.56 2 8-7 2.73 2 9-1 1.74 5 9-2 2.24 1 9-3 2.38 1 9-4 2.48 2 9-52.60 3 9-6 2.74 3 9-7 2.82 3 15-1  2.48 1 15-2  2.46 2 15-3  2.16 315-4  1.99 5 15-5  1.96 5 15-6  1.80 6

Careful examination of Table 6 reveals that the cellulose acetateshaving a DS from about 2.15 to about 2.42 that were produced byacetylation of cellulose dissolved in ionic liquids in the presence of asecondary component (Examples 3-6, 8, 9) all have an acetone solubilityrating of 1. That is, all of these samples yield transparent acetonesolutions in which there are no visible particles. In contrast,cellulose acetates produced by acetylation of cellulose dissolved inionic liquids in the absence of a secondary component (Examples 1 and 2)have acetone solubility ratings of 4-5 regardless of DS. For example,Example 1-2 (no secondary component) has a DS of 2.25 and this celluloseacetate forms a gel in acetone while Examples 8-3 and 9-2 (which includea secondary component) have a DS of 2.24 and these cellulose acetatesyield transparent acetone solutions. In agreement with what is knownabout cellulose acetates prepared by traditional methods, only one ofthe cellulose acetates examined (15-1, DS=2.48) has an acetonesolubility rating of 1. Example 15-3 (DS=2.16) has an acetone solubilityrating of 3, whereas Examples 4-3 and 8-2, which have similar DS values(DS=2.15), have acetone solubility ratings of 1.

This example shows that cellulose acetates produced by acetylation ofcellulose dissolved in ionic liquids in the presence of a secondarycomponent having a DS of about 2.1 to about 2.4 yield transparentacetone solutions. In the absence of a secondary component, none of thecellulose acetates listed in Table 6 yield transparent acetonesolutions. Furthermore, the DS range that yields transparent acetonesolutions when using cellulose acetates produced by acetylation ofcellulose dissolved in ionic liquids in the presence of a secondarycomponent is broader and lower relative to cellulose acetates producedby traditional methods. Without wishing to be bound by theory, thisevidence indicates that these solubility differences reflect adifference in copolymer compositions.

Example 16 Purification of [BMIm]acetate

To a 1 L 3-neck round bottom flask was added 360 mL of water, 1.30 g ofacetic acid, and 5.68 g of Ba(OH)₂—H₂O. The mixture was heated to 80°C., yielding a translucent solution. To this solution was added 300 g ofcommercial 1-butyl-3-methylimidazolium acetate (“[BMIm]OAc”) dropwiseover a period of 1 hour. The [BMIm]OAc contained 0.156 weight percentsulfur as determined by X-ray fluorescence (“XRF”). The solution washeld at 80° C. for an additional hour before allowing the solution tocool to room temperature. The solids formed during the reaction wereremoved by centrifuging before concentrating the solution in vacuo(60-65° C., 20-80 mm Hg) to a pale yellow liquid. The liquid wasextracted with two 300 mL portions of ethyl acetate (“EtOAc”). Theliquid was concentrated first at 60° C. and a pressure from 20-50 mm Hg,then at 90° C. and a pressure of 4 mm Hg, finally yielding 297.8 g of apale yellow oil. Proton NMR confirmed the formation of the [BMIm]OAcwhich, by XRF, contained 0.026 weight percent sulfur.

Example 17 Preparation of [BMIm]propionate

To a 1 L 3-neck round bottom flask was added 400 mL of water, 62.7 g ofacetic acid, and 267 g of Ba(OH)₂.H₂O. The mixture was heated to 74° C.,yielding a translucent solution. To this solution was added 100 g ofcommercial 1-butyl-3-methylimidazolium hydrogen sulfate (“[BMIm]HSO₄”)dropwise over a period of 1.75 hours. The solution was held at 74-76° C.for an additional 30 minutes before allowing the solution to cool toroom temperature and stand overnight (approximately 14 hours). Thesolids formed during the reaction were removed by filtration beforeconcentrating the solution in vacuo, which gave an oil containing solidsthat formed during concentration. The solids were removed bycentrifuging, resulting in an amber liquid. Additional product wasobtained by slurring the solids in EtOH and centrifuging. The liquidswere concentrated first at 60° C. and a pressure from 20-50 mmHg, thenat 90° C. and a pressure of 4 mm Hg, finally yielding 65.8 g of an amberoil. Proton NMR confirmed the formation of 1-butyl-3-methylimidazoliumpropionate (“[BMIm]propionate” or “[BMIm]OPr”) which, by XRF, contained0.011 weight percent sulfur.

Example 18 Preparation of [BMIm]formate

To a 300 mL autoclave was added 25 g of 1-butylimidazole, 45.4 g (3.75eq.) of methyl formate, and 21 mL of MeOH (2.58 eq.). The autoclave waspressurized to 1,035 kPa before heating the solution to 150° C. Thecontact solution was maintained at 150° C. for 18 hours. The solutionwas allowed to cool to room temperature before removing the volatilecomponents in vacuo. Proton NMR of the crude reaction mixture revealedthat 89% of the 1-butylimidazole was converted to1-butyl-3-methylimidazolium formate (“[BMIm]formate” or “[BMIm]OF”).Purified [BMIm]formate was obtained by removal of residual1-butylimidazole from the crude product by distillation.

Example 19 Conversion of [BMIm]formate to [BMIm]acetate Using MethylAcetate

To a 300 mL autoclave was added 25 g of [BMIm]formate, 50.3 g (5.0 eq.)of methyl acetate, and 50 mL of MeOH (9 eq.). The autoclave waspressurized to 1,035 kPa before heating the solution to 170° C. Thecontact solution was maintained 170° C. for 15.3 hours. The solution wasallowed to cool to room temperature before removing the volatilecomponents in vacuo. Proton NMR of the reaction mixture revealed that57% of the [BMIm]formate was converted to [BMIm]acetate.

Example 20 Conversion of [BMIm]formate to [BMIm]acetate Using AceticAnhydride

To a 25 mL single-neck round bottom flask was added 11.1 g of[BMIm]formate. 6.15 g of acetic anhydride was then added dropwise to the[BMIm]formate. Evolution of gas was noted during the addition as well aswarming of the solution (47° C.). The flask was then placed in apreheated 50° C. water bath for 45 minutes before applying a vacuum (4mm Hg) and heating to 80° C. to remove the volatile components. Analysisof the resulting liquid by ¹H NMR indicated 100% conversion of thestarting [BMIm]formate to [BMIm]acetate.

Example 21 Conversion of [BMIm]formate to [BMIm]acetate Using AceticAcid

To a 300 mL autoclave was added 25 g of [BMIm]formate, 87.4 g (6.3 eq.)of acetic acid, and 23.1 g of MeOH (5.3 eq.). The autoclave waspressurized to 1,035 kPa before heating the solution to 150° C. Thecontact solution was maintained at 150° C. for 14 hours. The solutionwas allowed to cool to room temperature before removing the volatilecomponents in vacuo. Proton NMR of the reaction mixture revealed that41% of the [BMIm]formate was converted to [BMIm]acetate.

Example 22 Conversion of [BMIm]acetate to [BMIm]formate Using MethylFormate

To a 1 L autoclave was added 100.7 g of [BMIm]acetate, 152.5 g (5 eq.)of methyl formate, and 200 mL of MeOH (9.7 eq.). The autoclave waspressurized to 1,035 kPa before heating the solution to 140° C. Thecontact solution was maintained at 140° C. for 18 hours. The solutionwas allowed to cool to room temperature before removing the volatilecomponents in vacuo. Proton NMR of the reaction mixture revealed that100% of the [BMIm]acetate was converted to [BMIm]formate.

Example 23 Comparison of High and Low Sulfur [BMIm]OAc 23A: Preparationof Cellulose Acetate with High Sulfur [BMIm]OAc

To a 100 mL 3-neck round bottom flask was added 32.75 g of commercial[BMIm]OAc having a relatively high sulfur content (0.156 weight percentsulfur; obtained from Fluka, a subsidiary of Sigma-Aldrich Inc., St.Louis, Mo., USA) and 1.72 g of cellulose powder. This mixture wasbriefly homogenized at ambient temperature before the flask was placedin a preheated 80° C. oil bath. The mixture was stirred at 80° C. and apressure of 2 mm Hg for a period of 1.75 hours. Approximately 15 minuteswere required to completely dissolve the cellulose. The straw coloredsolution was allowed to cool to room temperature and stand under vacuumovernight (approximately 14 hours).

To the mechanically stirred solution was added a solution of 210 mg ofMSA and 5.42 g of acetic anhydride (5 eq./AGU) dropwise over a period of23 minutes. At the end of the addition, the temperature of the contactmixture was 35° C. and the solution was dark amber in color. After 1.5hours from the start of the addition, 5.5 g of the contact mixture wasremoved and the product was isolated by precipitation in MeOH. Thecontact mixture was then heated to 50° C. (25 minute heat up) andstirred for 1.5 hours before 6.5 g of solution was removed and pouredinto MeOH. The remaining contact solution was heated to 80° C. (25minute heat up) and stirred for 2.5 hours before pouring into MeOH. Allof the solids obtained by precipitation in MeOH were isolated byfiltration, washed extensively with MeOH, and dried overnight at 50° C.and a pressure of 5 mm Hg.

23B: Preparation of Cellulose Acetate with Low Sulfur [BMIm]OAc

An identical reaction to 23A was conducted side-by-side using 37.02 g of[BMIm]OAc having a relatively low sulfur content (0.025 weight percentsulfur; prepared via the method described in example 16, above), 1.95 gof cellulose, 6.14 g of acetic anhydride, and 222 mg of MSA.

The amount of product isolated and the analysis of each product aresummarized below in Table 7.

TABLE 7 Yield and Properties of CA Prepared in [BMIm]OAc Entry Yield (g)DS Mn Mw Mz 23A-RT 0.37 2.53 15123 54139 135397 23A-50° C. 0.45 2.6512469 51688 123527 23A-80° C. 1.36 2.62 15828 85493 237785 23B-RT 0.290.80 14499 65744 301858 23B-50° C. 0.40 0.80 14768 57066 227833 23B-80°C. 1.26 0.76 16100 70293 325094

As can be seen from Table 7, above, the DS of the cellulose acetate madeusing the high sulfur [BMIm]OAc as solvent was higher and the molecularweight lower relative to the cellulose acetate made using the low sulfur[BMIm]OAc as solvent. Despite the increased temperature and extendedcontact time, the DS did not increase significantly above that observedafter 1.5 hours contact time at room temperature regardless of which[BMIm]OAc was used as the solvent. Another notable aspect of thisexample was the color of the solutions and products. The contactsolution involving high sulfur [BMIm]OAc solvent was black at alltemperatures while the contact solution involving low sulfur [BMIm]OAcsolvent retained the straw color typical of these solutions prior to theaddition of the anhydride. The cellulose acetate solids obtained fromthe high sulfur [BMIm]OAc solvent were brown to black in appearancewhile the CA solids obtained from the low sulfur [BMIm]OAc solvent werewhite and provided colorless solutions upon dissolution in anappropriate solvent.

This example illustrates that impurities (e.g., sulfur or halides) inthe high sulfur [BMIm]OAc can act as a catalyst in the esterification ofcellulose dissolved in the [BMIm]OAc. However, the same impuritiesnegatively impact the molecular weight and quality of the product insuch a manner that the cellulose acetate has no have practical value.When cellulose is dissolved in [BMIm]OAc containing little or none ofthese impurities, high-quality cellulose acetate can be obtained. Byintroduction of an appropriate catalyst, high quality cellulose acetatewith the desired DS can be obtained in a predictable manner.

Example 24 Acetylation of Cellulose In High Chloride [EMIm]OAc

1.19 g of cellulose was dissolved in 22.65 g of commercial [EMIm]OAchaving a high chloride content (0.463 weight percent chloride,determined by XRF analysis) following the general procedure described inExample 23 with the exception that the mixture was not homogenized priorto heating to 80° C. The straw colored solution was mechanically stirredand preheated to 80° C. Thereafter, a solution containing 141 mg of MSAand 3.76 g of acetic anhydride (5 eq./AGU) was added dropwise over aperiod of 10 minutes. By the end of the addition, the contact mixturebecame dark brown-black. The contact solution was stirred for 2.5 hoursbefore pouring into H₂O for precipitation. The resulting solids wereisolated by filtration, washed extensively with H₂O, and dried overnightat 50° C., 5 mm Hg. This yielded 1.57 g of a brown-black celluloseacetate powder. Analysis revealed that the cellulose acetate had a DS of2.21 and that the Mw was 42,206.

This example illustrates that [EMIm]OAc containing high levels ofhalides is not a suitable solvent for esterification of cellulose.

Example 25 Acetylation of Cellulose in [BMIm]Cl and [BMIm]OAc 25A:Acetylation of Cellulose in [BMIm]Cl

13.2 g of previously dried cellulose and 250.9 g of solid [BMIm]Cl(mp=70° C.) were combined in a glass jar. The glass jar was placed in apreheated 40° C. vacuum oven and heated to 80° C. over a period of 3hours. The sample was allowed to stand under vacuum at 80° C. for aperiod of approximately 14 hours before the jar was removed. The samplewas immediately homogenized, yielding a clear solution of cellulose.

To a 100 mL 3-neck round bottom flask was added 33.6 g of the cellulosesolution prepared above. The flask was placed in a preheated 80° C. oilbath and a vacuum was applied (7-8 mm Hg). The solution was then stirredfor a period of 21 hours while at 80° C. and under vacuum. The cellulosesolution was then allowed to cool to 38° C.; the temperature could notbe lowered further due to the solution viscosity. 5.3 g of aceticanhydride (5 eq./AGU) was then added dropwise over a period of 7minutes. The contact mixture was then stirred at a temperature of 32-35°C. for 2 hours. Thereafter, a small amount of the solution was removedand poured into MeOH resulting in precipitation of the celluloseacetate. The remaining contact mixture was then heated to 50° C. andheld at that temperature for 1.6 hours before removing a small amount ofthe solution, which was poured into MeOH to precipitate the celluloseacetate. The remaining contact mixture was then heated to 80° C. andheld at that temperature for 1.5 hours before allowing the solution tocool and adding 60 mL of MeOH to precipitate the cellulose acetate. Allthree samples were washed extensively with MeOH then dried at 50° C. anda pressure of 5 mm Hg overnight.

25B: Acetylation of Cellulose in [BMIm]Cl with Zn(OAc)₂

To a 100 mL 3-neck round bottom flask was added 31.3 g of the cellulosesolution prepared above. The same general protocol used in the previousreaction (25A) was followed with the exception that Zn(OAc)₂ (0.05eq./AGU) was added to the cellulose solution prior to cooling to 38° C.

25C: Acetylation of Cellulose in [BMIm]OAc

To a 100 mL 3-neck round bottom flask was added 27.41 g of low sulfur[BMIm]OAc (as prepared in example 16) and 1.44 g of cellulose. The flaskwas placed in a preheated 80° C. oil bath and the mixture was allowed tostir overnight (approximately 14 hours) under a 2 mm Hg vacuum.

After cooling the solution to room temperature (25.1° C.), Ac₂O (5eq./AGU) was added to the cellulose solution dropwise over a period of25 minutes. The contact mixture was then stirred for 1.8 hours at roomtemperature. Thereafter, a small portion of the solution was removed andpoured into MeOH to precipitate the cellulose acetate. The remainingcontact mixture was heated to 50° C. and maintained at that temperaturefor 1.5 hours before removing a small portion of the solution, which wasthen poured into MeOH to precipitate the cellulose acetate. Theremaining contact mixture was heated to 80° C. and maintained at thattemperature for 2.5 hours before cooling and pouring into MeOH. Allthree samples were washed extensively with MeOH then dried at 50° C. anda pressure of 5 mm Hg overnight.

25D: Acetylation of Cellulose in [BMIm]OAc with Zn(OAc)₂

To a 100 mL 3-neck round bottom flask was added 25.55 g of low sulfur[BMIm]OAc (as prepared in example 16, above) and 1.35 g of cellulose.The flask was placed in a preheated 80° C. oil bath and the mixture wasallowed to stir overnight (approximately 14 hours) under a 2 mm Hgvacuum. The same general protocol used in the previous reaction (25C)was followed, with the exception that Zn(OAc)₂ (0.05 eq./AGU) was addedto the cellulose solution prior to cooling to room temperature.

Analyses of the cellulose acetates isolated from these 4 comparativereactions (25A-25D) are summarized below in Table 8.

TABLE 8 Physical properties of CA prepared in [BMIm]Cl or [BMIm]OAcEntry Solvent Catalyst DS Mn Mw Mz 25A-RT [BMIm]Cl none 0.57 7753 1677732019 25A-50° C. [BMIm]Cl none 1.42 9892 19083 33019 25A-80° C. [BMIm]Clnone 2.27 11639 21116 34138 25B-RT [BMIm]Cl Zn(OAc)₂ 1.77 8921 1946836447 25B-50° C. [BMIm]Cl Zn(OAc)₂ 2.32 7652 18849 38367 25B-80° C.[BMIm]Cl Zn(OAc)₂ 2.75 7149 18964 38799 25C-RT [BMIm]OAc none 1.17 703941534 118265 25C-50° C. [BMIm]OAc none 1.17 7839 45116 136055 25C-80° C.[BMIm]OAc none 1.17 7943 48559 165491 25D-RT [BMIm]OAc Zn(OAc)₂ 2.278478 47730 125440 25D-50° C. [BMIm]OAc Zn(OAc)₂ 2.30 11017 53181 13661925D-80° C. [BMIm]OAc Zn(OAc)₂ 2.34 12096 56469 141568

This comparative example illustrates a number of important points. Inthe case of [BMIm]Cl, the DS of the cellulose acetate increases witheach contact time-temperature from 0.57 to 2.27. The same trend isobserved with [BMIm]Cl+Zn(OAc)₂ with the exception that the DS at eachcontact time-temperature is higher due to the Zn(OAc)₂, which acts as acatalyst. In the case of [BMIm]OAc, with or without Zn(OAc)₂ the DS doesnot significantly change from that obtained at room temperature withincreasing contact time-temperature; however, the total DS issignificantly increased by the action of the Zn(OAc)₂. This unexpectedobservation indicates that acetylation of cellulose dissolved in[BMIm]OAc is much faster at lower temperatures relative to that observedin acetylation of cellulose dissolved in [BMIm]Cl. It should also benoted that a transition metal like Zn is very effective in catalyzing orpromoting the acylation of cellulose dissolved in ionic liquids.Finally, it should also be noted that the molecular weights of thecellulose acetates obtained by acetylation of cellulose dissolved in[BMIm]OAc is significantly greater relative to when cellulose isdissolved in [BMIm]Cl.

Example 26 Preparation of Mixed Cellulose Esters

The following general procedure was used to prepare cellulose mixedesters. To a 100 mL 3-neck round bottom flask was added the desiredamount of a selected 1-butyl-3-methylimidazolium carboxylate. Whilestirring at room temperature, 5 weight percent cellulose was slowlyadded to the ionic liquid. After the cellulose was dispersed in theionic liquid, the flask was placed under vacuum (2-5 mm Hg) and thecontact mixture was heated to 80° C. The contact solution was thenstirred for a period of approximately 2 hours before adding 0.1 eq./AGUof Zn(OAc)₂. The contact solution was stirred for approximately 30minutes before the solution was allowed to cool to room temperature andstand overnight (approximately 14 hours).

The contact solution was then placed under N₂, followed by the dropwiseaddition of 5 eq./AGU of the desired carboxylic anhydride. When theaddition was complete, the flask was placed in a preheated 40° C. oilbath. The contact mixture was stirred for 5 hours before the solutionwas allowed to cool and poured into MeOH for precipitation. Theresulting solids were isolated by filtration, washed extensively withMeOH, and dried in vacuo at 50° C. and a pressure of 5 mm Hg. Theproducts were then characterized by ¹H NMR, the results of which aresummarized below in Table 9.

TABLE 9 Cellulose Esters Prepared in Different Alkyl ImidazoliumCarboxylates Entry Ionic liquid Anhydride DS_(Total) DS_(Ac) DS_(Pr)DS_(Bu) 1 [BMIm]OAc Bu₂O 2.40 2.43 — 0.45 2 [BMIm]OBu Ac₂O 2.43 2.30 —0.70 3 [BMIm]OPr Bu₂O 2.52 — 1.95 1.05

Note that in Table 9, above, the DS of the individual substituents havebeen normalized to 3.0 for comparison purposes. As this exampleillustrates, when cellulose is dissolved in an alkyl imidazoliumcarboxylate and contacted with a carboxylic anhydride containing adifferent acyl group from the anion of the ionic liquid, the product isa mixed cellulose ester. That is, the cellulose substituents come fromthe added anhydride and from the alkyl imidazolium carboxylate. Ineffect, the alkyl imidazolium carboxylate is acting as an acyl donor tothe cellulose.

Example 27 Removal of Carboxylic Acid

To each vessel of a 4 vessel Multimax high pressure reactor equippedwith an in situ infrared probe was added previously dried [BMIm]OAc, 1molar equivalent of acetic acid based on ionic liquid, different molaramounts of MeOH based on acetic acid, and, optionally, a catalyst (2 mol%). The pressure in each vessel was increased to 5 bar over a 3 minuteperiod, followed by increasing the contact temperature to 140° C. over a25 minute period. The contact mixtures were then held at 140° C. for10-15 hours as the reaction in each vessel was monitored by infraredspectroscopy. The vessels were then allowed to cool to 25° C. over a 30minute period. The contents of each vessel were then concentrated invacuo to remove all volatile components before analyzing each sample byproton NMR. FIG. 16 shows a plot of weight percent acetic acid versustime as determined by infrared spectroscopy; the final concentration ofacetic acid was confirmed by ¹H NMR. FIG. 16 shows that in all cases,the reactions were complete within 9-10 hours. The most significantfactor affecting the rates and extent of reaction was the number ofmolar equivalents of MeOH. The weight percent of acetic acid remainingin the [BMIm]OAc ranged from 7.4 weight percent to 2.2 weight percent.

With typical distillation techniques, it is extremely difficult to getexcess carboxylic acid concentration below 1 molar equivalent based oncarboxylated ionic liquid. In the case of acetic acid in [BMIm]OAc, thiscorresponds to about 23 weight percent acetic acid. This example showsthat, by conversion of the acetic acid to methyl acetate, which is muchmore easily removed, the amount of residual acetic acid can be reducedwell below 23 weight percent. The amount of acetic acid removed willdepend upon several factors, including the amount of acetic acidinitially present, concentration of MeOH, contact times, and contacttemperature. As shown in this example, it is not necessary to remove allof the residual carboxylic acid; in many instances, it is desirable toretain residual carboxylic acid.

Example 28 Solubility of Cellulose in Ionic Liquid

Samples of 1-butyl-3-methylimidazolium acetate containing differentamounts of acetic acid in 2 ounce jars were dried at 80° C.±5° C. at apressure of about 3 mm Hg overnight (approximately 14 hours). Examples28-1 through 28-5 were prepared by the method of Example 27. Examples28-6 through 28-8 were prepared by adding a known amount of acetic acidto neat [BMIm]OAc (see Table 10). Cellulose (5 weight percent, DP 335),was added to each [BMIm]OAc sample, followed by brief homogenization ofeach sample. Each sample was then transferred to a microwave reactionvessel, which was then capped with an air tight lid and placed in a 48cell microwave rotor. The rotor was placed in a Anton Paar Synthos 3000microwave and the cellulose-[BMIm]OAc mixtures were heated to 100° C.using a 3 minute ramp and held for 10 minutes before heating to 120° C.using a 3 minute ramp and held for 5 minutes. Inspection of each vesselindicated that the cellulose in each sample was dissolved in the[BMIm]OAc.

TABLE 10 Solubility of Cellulose in [BMIm]OAc Example HOAc (wt %) IL (g)Soluble 28-1 2.2 6.16 y 28-2 2.8 8.78 y 28-3 5.8 8.48 y 28-4 6.6 8.48 y28-5 7.4 8.15 y 28-6 10.0 10.23 y 28-7 12.5 10.26 y 28-8 14.5 10.18 y

The foregoing two examples illustrate that excess residual carboxylicacid in ionic liquids can be reduced by the method of Example 27 andthat the recycled ionic liquid containing residual carboxylic acid canthen be used to dissolve cellulose so that the solutions can be used forpreparing cellulose esters. This example also illustrates that cellulosecan be dissolved in an ionic liquid containing up to about 15 weightpercent carboxylic acid.

Example 29 Recycling of Ionic Liquid

To a 500 mL flat bottom kettle was added 299.7 g of [BMIm]OAc. A 4-necktop was placed on the kettle and the kettle was fitted with an N₂/vacuuminlet, a React IR 4000 diamond tipped IR probe, a thermocouple, andequipped for mechanical stirring. The kettle contents were placed undervacuum (approximately 4.5 mm Hg) and heated to 80° C. using an oil bath.The removal of water from the [BMIm]OAc was followed by analysis byinfrared spectroscopy (FIG. 17). After about 16 hours, the oil bath wasremoved and the kettle contents were allowed to cool to roomtemperature.

To the ionic liquid was added 3.77 g of Zn(OAc)₂ (0.1 eq.). The mixturewas stirred for about 75 minutes to allow the Zn(OAc)₂ to dissolvebefore slowly adding 33.3 g (10 weight percent) of previously driedcellulose (DP 335) over a 26 minute period. The mixture was stirred atroom temperature for about 4 hours, after which time no particles orfiber were visible in the translucent solution; infrared spectroscopyindicated that all of the cellulose was dissolved (FIG. 18). Thesolution was then heated to 80° C. By the time the temperature reached60° C., the translucent solution was completely clear. After reaching80° C., the solution was cooled to room temperature.

To the cellulose-[BMIm]OAc solution was added 104.9 g of Ac₂O (5 eq.)dropwise over a 70 minute period. During the Ac₂O addition, the contacttemperature rose from an initial value of 21.4° C. to a maximum value of44.7° C. Infrared spectroscopy indicated that the Ac₂O was consumednearly as fast as it was added (FIG. 19). When all of the Ac₂O wasadded, the contact temperature immediately began to decline and thecontact mixture went from a fluid liquid to a flaky gel. Stirring wascontinued for an additional 3.5 hours, but no changes were observed byinfrared spectroscopy.

The gel was then added to 800 mL of MeOH while stirring, resulting inthe precipitation of a white powder. After separation by filtration, thesolids were then washed 3 times with approximately 800 mL portions ofMeOH, then 1 time with approximately 900 mL of MeOH containing 11 weightpercent of 35% H₂O₂. The solids were then dried at 40° C. and a pressureof 3 mm Hg yielding 60.4 g of a white solid. Analysis by proton NMR andGPC revealed that the solid was a cellulose triacetate (DS=3.0) having aMw of 58,725. The cellulose triacetate (13.6 weight percent) wascompletely soluble in 90:10 CH₂Cl₂:MeOH, from which clear films can becast. Such films are useful in constructing liquid crystalline displaysand in photographic film base.

The precipitation and wash liquids from the cellulose triacetateisolation were concentrated in vacuo at 50° C. until the vacuum droppedto about 3 mm Hg, which yielded 376.6 g of a liquid. Proton NMRindicated that the liquid was [BMIm]OAc containing approximately 17weight percent excess acetic acid. To a 1.8 L autoclave was added the376.6 g of recovered [BMIm]OAc along with 483.8 g of MeOH. The pressurein the autoclave was adjusted to 100 psi with N₂ before the vesselcontents were heated to 140° C. and held for 9 hours. After cooling toroom temperature, the volatile components were removed in vacuo, whichproduced 299.8 g of a liquid. Proton NMR showed the liquid to be[BMIm]OAc containing 2.6 weight percent excess acetic acid. When theweight of the initial [BMIm]OAc was corrected for water content, theamount of recycled [BMIm]OAc corresponds to 100% recovery.

This example illustrates that cellulose triacetate can rapidly beprepared from cellulose that has been dissolved in ionic liquids. Thisexample also indicates that excess carboxylic acid can be removed fromthe ionic liquid and the recycled ionic liquid can be recovered in highyield. The recycled ionic liquid can then be used to dissolve celluloseso that the solutions can be used again for preparing cellulose esters.

Example 30 Anion Exchange to Form Carboxylated Ionic Liquid

To a vial containing a small magnetic stir bar was added 4.2 g of[BMIm]formate. An iC10 diamond tipped IR probe was inserted into thevial so that the reaction could be monitored in situ by infraredspectroscopy. To the [BMIm]formate was added 0.5 eq. of Ac₂O in oneportion. As FIGS. 20 and 21 illustrate, 50% of the [BMIm]formate wasalmost immediately converted to [BMIm]OAc. Additional spectra werecollected to allow the system to stabilize before adding another 0.5 eq.of Ac₂O in one portion. Infrared spectroscopy indicated that theremaining [BMIm]formate was almost immediately converted to [BMIm]OAc.

This example shows that [BMIm]formate is rapidly converted to [BMIm]OAcwith the addition of Ac₂O. The reaction rate is so rapid that the[BMIm]formate can be titrated with Ac₂O until no gas is evolved.

Example 31 Effect of MeOH During Anion Exchange

To a vial containing a small magnetic stir bar was added 3.15 g of[BMIm]formate. An iC10 diamond tipped IR probe was inserted into thevial so that the reaction could be monitored in situ by infraredspectroscopy. To the [BMIm]formate was added 2 eq. of MeOH. After thesystem thermally stabilized, 1 eq. of Ac₂O was added to the[BMIm]formate in one portion. As FIGS. 22 and 23 illustrate, infraredspectroscopy indicated that the [BMIm]formate was almost immediatelyconverted to [BMIm]OAc.

This example shows that the reaction of [BMIm]formate with Ac₂O to form[BMIm]OAc is much faster than the reaction of Ac₂O with MeOH to formMeOAc. Hence, it is not necessary to remove MeOH from [BMIm]formateprior to converting the [BMIm]formate to [BMIm]OAc.

Example 32 Effects of Water Modification and MSA

A 3-neck 250 mL round bottom flask, fitted with two double neck adaptersfor a total of five ports, was equipped for mechanical stirring, andfurther included an iC10 diamond tipped IR probe (Mettler-ToledoAutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flaskwas added 62.37 g of [BMIm]OAc.

To 5.06 g (7.5 weight percent) of cellulose (DP 335) was added 20.68 gof water. After hand mixing, the cellulose was allowed to stand in thewater for 65 minutes at 60° C. before filtering, which yielded 10.78 gof a wet cellulose cake. The water-wet cellulose was then added in smallportions to the [BMIm]OAc over a period of 5 minutes. Within 5 minutes,the cellulose was well dispersed in the ionic liquid (a few small clumpswere visible). The mixture was stirred for 7 minutes before a preheated80° C. oil bath was raised to the flask. The mixture was then stirredfor 28 minutes (visually, nearly all of the cellulose was dissolved)before slowly placing the flask contents under vacuum with the aid of ableed valve (FIG. 24). After 1.5 hours, the vacuum was at 1.9 mm Hg. Theclear mixture was then stirred overnight under vacuum at 80° C.

The clear solution was allowed to cool to room temperature after 15hours and 45 minutes from the point of cellulose addition. Thereafter, amixture of 12.11 g (3.8 eq.) of Ac₂O and 600 mg of MSA was added to thesolution dropwise over a period of 28 minutes. The maximum temperaturereached during the Ac₂O addition was 46° C. Eight minutes aftercompleting the Ac₂O addition, a preheated 50° C. oil bath was raised tothe flask. The mixture was stirred for 16 minutes, and then 1.46 g ofwater was slowly added to the solution over a period of 2 minutes. Thesolution was then stirred for 17 minutes followed by adding anadditional 0.47 g of water. The solution was then stirred for 5 hoursand 9 minutes before cooling the solution to room temperature. Thereaction was sampled (see FIG. 25) throughout the contact period byremoving 6 to 10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed once with a 100mL portion of MeOH then twice with 100 mL of MeOH containing 8 weightpercent of 35% H₂O₂. The samples were then dried at 60° C. and apressure of 5 mm Hg overnight.

This example illustrates a number of benefits of the methods employedherein. As can be seen from FIG. 24, water-wet cellulose can be readilydissolved in carboxylated ionic liquid even when a significant amount ofwater still remains in the ionic liquid. As shown in FIG. 25, the rateof reaction in the acylation of this cellulose in a carboxylated ionicliquid is very rapid; a significant concentration of Ac₂O is neverobserved indicating that the Ac₂O is consumed nearly as fast as it isadded. The rapid rates of reaction can lead to a much different monomerdistribution relative to that observed in other ionic liquids. Forexample, FIG. 26 compares the proton resonances of the protons attachedto the anhydroglucose rings of cellulose acetates (DS=2.56) preparedfrom cellulose dissolved in [BMIm]OAc (top spectrum) and dissolved in[BMIm]Cl (bottom spectrum). The major resonances in the top spectrumcentered near 5.04, 5.62, 4.59, 4.29, 4.04, 3.73, and 3.69 correspond totrisubstituted monomers. In the bottom spectrum, there are much less ofthese resonances relative to the other type of monomer resonances. Thisdiscovery is significant in that the rapid rates of reaction provide ameans to produce nonrandom cellulose ester copolymers with differentlevels of block segments. The extent and the size of the block segmentsdepends upon factors such as mixing, prior water treatment or no watertreatment of the cellulose, concentration and type of catalyst, contacttemperature, and the like.

As shown in FIG. 25, 3 samples were taken prior to the addition ofwater. These 3 samples ranged in DS from 2.48-2.56 and, at 10 weightpercent in acetone, they were soluble giving slightly hazy solutions(solubility rating of 2). In contrast, the 2 samples taken after wateraddition (DS about 2.52) were insoluble in acetone (solubility rating of6). FIG. 27 compares the ring proton resonances for cellulose acetatesprepared from cellulose dissolved in [BMIm]OAc before and after additionof water. The top spectrum corresponds to a cellulose acetate afterwater addition (DS=2.53) and the bottom spectrum corresponds to acellulose acetate before water addition (DS=2.56). The differencesbetween these 2 spectra are consistent with different monomercompositions in the copolymers.

Example 33 Production of Cellulose Triacetate in [EMIm]OAc

To a 3-neck 100 mL round bottom flask equipped for mechanical stirringand having an N₂/vacuum inlet was added 34.63 g of1-ethyl-3-methylimidazolium acetate (“[EMIm]OAc”). While stirringrapidly, 6.11 g (15 weight percent) of dry cellulose powder (DP 335) wasadded to the flask. The flask was then placed in a 90° C. oil bath andthe mixture was stirred for 10 minutes, followed by application ofvacuum (2 mm Hg). After 50 minutes, the oil bath temperature wasincreased to 100° C. After 2 hours and 25 minutes, the oil bath wasturned off and the solution was left standing under vacuum overnight.

To the cellulose solution was added a mixture of 731 mg of MSA and 19.24g (5 eq.) of Ac₂O dropwise over a period of 40 minutes. Initially, thesolution was stirred slowly so that the solution did not bunch aroundthe stir shaft. As the Ac₂O was added, the solution viscosity dropped;after adding about 5 mL, the solution stirred easily and the stir ratewas increased. During the addition, the solution viscosity did notincrease and no localized gels were observed until the last few drops ofAc₂O were added. At this point the entire contact mixture suddenlygelled. The contact temperature rose from 24.1° C. to 47.5° C. by theend of addition. During the addition, there was little change in thecolor of the solution. After the reaction mixture gelled, 11.54 g of thereaction mixture was removed with a spatula and solids were obtained byprecipitation in MeOH (Sample 1). The flask containing the remainingreaction mixture was then placed in a preheated 50° C. oil bath. After20 minutes at 50° C., there was no evidence of the gel softening. Hence,the gel was allowed to cool to room temperature and 50 mL of MeOH wasadded to the flask. The flask contents were then placed into 400 mL ofMeOH, which yielded a white precipitate (Sample 2). Both fractions wereprocessed by stirring the initial slurry for approximately 1 hour beforeisolating the solids by filtration. The solids were washed by takingthem up in 300 mL of MeOH and stirring the slurry for approximately 1hour before the solids were isolated by filtration. The solids weretwice taken up in 300 mL of 12:1 MeOH:35% H₂O₂ and the slurry wasstirred for approximately 1 hour before the solids were isolated byfiltration. The solids were then dried overnight at 50° C. and apressure of about 20 mm Hg.

The combined yield for Samples 1 and 2 was 10.2 g of a white solid.Analysis by ¹H NMR showed that Samples 1 and 2 were identical and thatthey were cellulose triacetates with a DS of 3.0. By GPC, both sampleshad a Mw of about 54,000.

This example shows that cellulose triacetate can rapidly be preparedfrom cellulose dissolved in [EMIm]OAc. Cellulose triacetate can be usedto prepare film useful in liquid crystalline displays and photographicfilm base.

Example 34 Immiscible Co-Solvent Effect on IL Viscosity

To a 3-neck 50 mL round bottom flask equipped for mechanical stirringand having an N₂/vacuum inlet was added 20.03 g of [EMIm]OAc. Whilestirring rapidly, 1.05 g of dry cellulose powder (DP 335) was added tothe flask. The flask was then placed under vacuum (2 mm Hg) and placedin an oil bath preheated to 90° C. After 1 hour and 45 minutes, the oilbath temperature was increased to 100° C. and stirred for an additional55 minutes (2 hours and 40 minutes total contact time) before allowingthe solution to cool to ambient temperature while under vacuum.

To the resulting cellulose solution was added 20 mL of methyl acetate,yielding a 2-phase reaction mixture. While stirring rapidly, a mixtureof 131 mg of MSA and 4.63 g of Ac₂O was added dropwise to the solutionover a period of 10 minutes. The contact temperature was increased from23.3° C. to 35.4° C. and, at the end of the addition, the contactmixture was a single phase whose viscosity was much lower than that ofthe original cellulose-[EMIm]OAc solution. Twenty-five minutes afterbeginning the addition, the flask was placed in a preheated 50° C. oilbath. The contact mixture was stirred for 2 hours at 50° C. andthereafter allowed to cool to ambient temperature over a period of 50minutes. The product was precipitated in 350 mL of MeOH and the slurrywas stirred for approximately 1 hour before the solids were isolated byfiltration. The solids were then washed by taking them up in 300 mL ofMeOH and stirring the slurry for about 1 hour before the solids wereisolated by filtration. Twice, the solids were taken up in 300 mL of12:1 MeOH:35% H₂O₂ and the slurry was stirred for about 1 hour beforethe solids were isolated by filtration. The solids were then driedovernight at 50° C. and a pressure of about 20 mm Hg, which yielded 1.68g of a white solid. Analysis by ¹H NMR revealed that the solid was acellulose acetate having a DS of 2.67. Analysis by GPC indicated thatthe cellulose acetate had a Mw of 51,428 and a Mw/Mn of 4.08.

This example shows that a cellulose solution in an ionic liquid can becontacted with an immiscible or sparingly soluble co-solvent withoutcausing precipitation of the cellulose. Upon contact with an acylatingreagent, the cellulose is esterified, thus changing the solubility ofthe now cellulose ester-ionic liquid solution with the formerlyimmiscible co-solvent so that the contact mixture becomes a singlephase. The resulting single phase has a much lower solution viscositythan the initial cellulose-ionic liquid solution. This discovery issignificant in that highly viscous cellulose solutions can now be usedto make cellulose esters while still maintaining the ability to mix andprocess the solution. This discovery also provides a way to processhighly viscous cellulose-ionic liquid solutions at lower contacttemperatures. The cellulose ester product can be isolated from the newsingle phase by conventional means. The cellulose ester product hasdesirable degrees of substitution, molecular weights, and solubility insolvents such as acetone, and can be readily melt processed whenplasticized with plasticizers such as diethyl phthalate and the like.

Example 35 Immiscible Co-Solvent Biphasic to Single Phase

A 3-neck 100 mL round bottom flask containing 28.84 g of a 5 weightpercent cellulose solution in [BMIm]Cl was equipped for mechanicalstirring and with an N₂/vacuum inlet. The flask was placed in apreheated 80° C. oil bath and the flask contents were placed undervacuum (approximately 7 mm Hg) for 2 hours. To the solution was added 25mL of methyl ethyl ketone that had been previously dried over 4 Amolecular sieves resulting in two well defined phases. To the biphasicmixture was added 4.54 g of Ac₂O while stirring vigorously. After about75 minutes, the contact mixture appeared to be homogeneous. After 2.5hours, the contact mixture was allowed to cool to room temperature.Phase separation did not occur even when a small amount of water andmethyl ethyl ketone was added to the homogeneous mixture. The productwas isolated by addition of the contact mixture to 200 mL of MeOHfollowed by filtration to separate the solids. The solids were washedtwice with MeOH and three times with water before they were dried at 50°C. and a pressure of about 5 mm Hg. Analysis by ¹H NMR and by GPCrevealed that the product was a cellulose acetate with a DS of 2.11 andMw of 50,157.

This example shows that a cellulose solution in an ionic liquid, such as[BMIm]Cl, can be contacted with an immiscible or sparingly solubleco-solvent, such as methyl ethyl ketone, without causing precipitationof the cellulose. Upon contact with an acylating reagent, the celluloseis esterified, which changes the solubility of the now celluloseester-ionic liquid solution with the formerly immiscible co-solvent sothat the contact mixture became a single phase from which the celluloseester could be isolated by precipitation with an alcohol.

Example 36 Color of Cellulose Esters

Color development during esterification of cellulose dissolved in ionicliquids depends on a number of factors. These factors include the typeof ionic liquid used to dissolve the cellulose, impurities contained inthe ionic liquid, type of cellulose, the presence or absence of binarycomponents (see, e.g., Example 3), cellulose dissolution contact timeand temperature, and esterification contact time and temperature, amongothers. Understanding these factors and the mechanisms involved in colorformation is the best way to prevent color formation. However, even whenthe best practices are followed, colored product is still oftenobtained. The inventors have found that color formation can be reducedby contacting the cellulose ester with a bleaching agent while dissolvedin ionic liquid and/or after separation of the cellulose ester from theionic liquid.

Table 11, below, compares the color values of several cellulose estersprepared according to the following general method. To a 7.5 weightpercent solution of cellulose dissolved in ionic liquid was added amixture of 2.9 equivalents of acylating reagent (i.e., acetic anhydride,propionic anhydride, and/or butyric anhydride) and 0.1 equivalents of abinary component. The type of ionic liquid and binary component (ifpresent) employed for each sample are indicated in Table 11, below.After 65 minutes, in situ IR indicated that the reaction was complete.Entries 1-6 of Table 11 were then isolated by precipitation in water,washed with water, and dried.

Entry 9 of Table 11 was subjected to a bleaching process while still insolution. Thus, to the solution prepared as described above was added0.75 weight percent of a 2.25 weight percent solution of potassiumpermanganate dissolved in methanol. The mixture was stirred for 2 hoursbefore the cellulose ester was isolated by precipitation in water,washed with water, and dried.

Entries 7, 8, and 10-16 of Table 11 were subjected to a bleachingprocess following isolation. Thus, after completing the reactiondescribed above, the cellulose ester was isolated from the ionic liquidby precipitation in methanol followed by washing with water. Thereafter,the resulting solids were twice taken up in 300 mL of 12:1 MeOH:35% H₂O₂and the slurry was stirred for about 1 hour before the solids wereisolated by filtration.

TABLE 11 Color Evaluation of Cellulose Ester Solutions Ionicliquid-(binary Cellulose Entry L* a* b* ΔE component) Ester^(‡) Bleach 197.65 −2.24 11.07 11.54 [BMIm]Cl-(MSA)^(†) CA None 2 94.28 −1.85 17.8318.83 [BMIm]Cl-(MSA) CA None 3 93.56 −1.74 17.84 19.06 [BMIm]Cl-(MSA) CANone 4 46.56 41.45 77.89 103.19 [BMIm]OAc-(MSA) CA None 5 50.35 35.4489.8 108.59 [BMIm]OAc CA None 6 74.52 12.66 85.28 89.91 [BMIm]OAc CAPNone 7 96.89 −1.44 10.10 10.68 [BMIm]Cl-(MSA) CA H₂O₂ 8 98.24 −1.09 4.374.85 [BMIm]Cl-(MSA) CA H₂O₂ 9 98.37 −1.04 5.69 6.02 [BMIm]Cl-(MSA) CAKMnO₄ 10 98.43 −3.00 10.72 11.24 [EMIm]OAc CA H₂O₂ 11 98.10 −3.06 10.3410.95 [BMIm]OAc CA H₂O₂ 12 98.44 −1.51 5.87 6.27 [BMIm]OBu CAB H₂O₂ 1397.91 −2.43 10.68 11.15 [EMIm]OAc-(MSA) CA H₂O₂ 14 99.44 0.00 0.58 0.87[BMIm]OAc—(Zn(OAc)₂) CA H₂O₂ 15 99.02 0.05 1.63 1.94[BMIm]OAc—(Zn(OAc)₂) CA H₂O₂ 16 99.32 −0.48 1.98 2.16 [BMIm]OPr-(MSA) CPH₂O₂ ^(†)MSA = methane sulfonic acid ^(‡)CA = cellulose acetate CAP =cellulose acetate propionate CAB = cellulose acetate butyrate CP =cellulose propionate

As can be seen in Table 11, comparing entries 1-3 to entries 4-6 (eachhaving no bleaching), it is evident that more color is created duringcellulose esterification when the anion of the ionic liquid is acarboxylate compared to when the anion is a halide. When the anion was ahalide, and in the absence of bleaching, the L* and ΔE values rangedfrom 93.6-97.7 and 19.1-11.5, respectively (entries 1-3). Bleaching withH₂O₂ after separation of the cellulose ester from the ionic liquidincreased the a* values and decreased the b* values, resulting inimprovement of color which is reflected in a lower ΔE values (entries 7and 8). Bleaching the cellulose ester while it is dissolved in the ionicliquid led to a similar improvement in color (entry 9). In this case, L*and a* increased while b* decreased resulting in a ΔE value of 6.02.

When the anion was a carboxylate, in the absence of bleaching, L* and ΔEranged from 46.6-74.5 and 108.6-89.9, respectively (entries 4-6).Bleaching with H₂O₂ after separation of the cellulose ester from theionic liquid led to a dramatic improvement in color. The L* valuesincreased while the a* and b* values decreased, resulting in ΔE valuesof 0.9-11.2 (entries 10-16). Accordingly, this example illustrates thatcontacting a cellulose ester with a bleaching agent while dissolved inionic liquid or after separation of the cellulose ester from the ionicliquid can lead to very significant improvements in color.

Example 37 Viscosities of Cellulose-Ionic Liquid Solutions with MiscibleCo-Solvents

Solutions of cellulose dissolved in [BMIm]Cl containing different levelsof acetic acid were prepared according to the following generalprocedure. [BMIm]Cl was added to a 3-neck, 50 mL round bottom flaskequipped for mechanical stirring and with an N₂/vacuum inlet. The flaskwas placed in a preheated 80° C. oil bath and the flask contents wereplaced under vacuum (0.8 mm Hg) for 1.7 hours. Thereafter, either 0, 5,or 10 weight percent of acetic acid was added to the solution beforeallowing it to cool to room temperature. Next, 5 weight percent ofcellulose was added to the solution and was then heated again to 80° C.The mixture was stirred until a homogeneous solution was obtained (about80 minutes). The solution was then cooled to room temperature.

FIG. 28 compares the viscosities of cellulose solutions containing noacetic acid, 5 weight percent acetic acid, and 10 weight percent aceticacid at 25, 50, 75, and 100° C. As illustrated in FIG. 28, the viscosityof the cellulose-[BMIm]Cl-5 weight percent acetic acid solution issignificantly less than that of cellulose-[BMIm]Cl at all temperatures.For example, at 25° C. and 0.2 rad/sec, the viscosity of thecellulose-[BMIm]Cl-5 weight percent acetic acid solution is 466 poiseversus 44,660 poise for the cellulose-[BMIm]Cl solution. Comparing theviscosities of the cellulose-[BMIm]Cl-10 weight percent acetic acidsolution to the cellulose-[BMIm]Cl-5 weight percent acetic acid andcellulose-[BMIm]Cl solutions at 25° C., it is evident that the viscosityof the cellulose-[BMIm]Cl-10 weight percent acetic acid solution is lessthan that of the cellulose-[BMIm]Cl solution but greater than that ofthe cellulose-[BMIm]Cl-5 weight percent acetic acid solution. At 25° C.and 0.2 rad/sec, the viscosities of the cellulose-[BMIm]Cl-10 weightpercent acetic acid, cellulose-[BMIm]Cl-5 weight percent acetic acid,and cellulose-[BMIm]Cl solutions are 22,470, 466, and 44,660 poise,respectively. With increasing temperature, the differences in theviscosities between the cellulose-[BMIm]Cl-10 weight percent acetic acidand cellulose-[BMIm]Cl solutions diminish and the observed viscositiesapparently depend upon the shear rate.

This example shows that the viscosity of a cellulose-ionic liquidsolution can be dramatically altered by adding a miscible co-solventsuch as a carboxylic acid to the solution. The viscosity drops withincreasing miscible co-solvent reaching a minimum before increasingagain as additional co-solvent is added.

Example 38 Viscosities of Cellulose-Ionic Liquid Solutions withImmiscible Co-Solvents

In order to determine the impact of an immiscible co-solvent (whichtends to form two layers with the initial cellulose-ionic liquidsolution) on solution viscosity, it is necessary to convert thecellulose to a cellulose ester prior to making the viscositymeasurement.

A cellulose solution was prepared as follows. To a 3-neck, 100 mL roundbottom flask equipped for mechanical stirring and with an N₂/vacuuminlet was added 33.18 g of [BMIm]CL. While stirring rapidly, 1.75 g ofdry cellulose (5 weight percent) were added to the flask. The flask wasthen placed under vacuum (2 mm Hg) and placed in an oil bath preheatedto 80° C. After 30 minutes in the oil bath, all of the cellulose wasdissolved. The oil bath and stirring were turned off and the solutionwas left under vacuum overnight.

To the resulting cellulose solution was added 30 mL of methyl ethylketone resulting in a 2-phase reaction mixture. While stirring rapidly,a mixture of 104 mg of MSA and 5.51 g of Ac₂O was added dropwise over aperiod of 3 minutes. At the end of the addition, the reaction mixturehad two phases. After stirring for about 70 minutes from the start ofaddition, the reaction mixture was a single phase; the viscosity of thephase was much less than that of the original cellulose solution.Stirring was continued for an additional 150 minutes before 10.9 g ofthe solution was removed for viscosity measurements. The remainingsolution was then cooled to room temperature and the product wasisolated by precipitating in 350 mL of MeOH. The resulting slurry wasstirred for about 1 hour before the solids were isolated by filtration.The solids were then washed 4 times with 250 mL of MeOH. The solids werethen dried overnight at a temperature of 50° C., and a pressure of 5 mmHg, which gave 1.66 g of a white solid. Analysis revealed that the solidwas the expected cellulose acetate. A second reaction was conducted inthe same fashion except that the co-solvent (i.e., methyl ethyl ketone)was omitted. Again, a sample was removed for viscosity measurements justprior to precipitation of the cellulose acetate.

FIG. 29 compares the solution viscosity of the contact mixtures with andwithout an immiscible co-solvent at 25° C. As can be seen in FIG. 29,inclusion of an immiscible co-solvent dramatically reduces the viscosityof the solution. For example, at 25° C. and 1 rad/sec, inclusion ofmethyl ethyl ketone resulted in a solution with a viscosity of 24.6poise versus 6,392 poise for the solution without methyl ethyl ketone.

Example 39 Impact of Miscible Co-Solvents on Reaction Rates and DS

The impact of miscible co-solvents on reaction rates and the totaldegree of substitution (“DS”) were determined by comparing samplesprepared according to the following methods. A 3-neck 100 mL roundbottom flask was equipped with a double neck adapter giving four ports,an iC10 diamond tipped IR probe, for mechanical stirring, and aN₂/vacuum inlet. To the flask was added 50.15 g of1-butyl-3-methylimidazolium propionate (“[BMIm]OPr”). While stirringrapidly, 4.07 g of cellulose (7.5 weight percent) was added to the[BMIm]OPr at room temperature. Vacuum was applied with the aid of ableed valve. After reaching 0.6 mm Hg, a preheated 80° C. oil bath wasraised to the flask. A clear solution was obtained 8 minutes afterraising the oil bath. Stirring was continued for an additional 2.8 hoursbefore the solution was allowed to cool to room temperature and standunder N₂ for 12 hours.

To the cellulose solution at room temperature was added a mixturecontaining 12.09 g of propionic anhydride (3.7 eq.) and 482 mg of MSA(0.2 eq.) dropwise over a period of 20 minutes. During the course of thereaction, aliquots were removed and the product was isolated byprecipitation in 200 mL of methanol and filtering. The reaction wascomplete 20 minutes after the end of addition. The experiment wasterminated and the remaining reaction mixture was processed in the samemanner as the aliquots. The solid from each sample was washed 3 timeswith 200 mL portions of methanol then 1 time with 250 mL of methanolcontaining 8 weight percent of 35 weight percent H₂O₂. The white solidswere then dried at a temperature of 60° C. and a pressure of 5 mm Hg. Asecond set of samples was prepared following the same procedure asoutlined above, with the exception that the [BMIm]OPr contained 11.9weight percent propionic acid as a miscible co-solvent.

FIG. 30 shows a plot of absorbance for a band at 1212 cm⁻¹ (propionateester and propionic acid) versus contact time for each of the samplesprepared as described above. The DS indicated in FIG. 30 correspond tothe DS values for the samples obtained in each procedure. Relative tothe reaction of cellulose dissolved in [BMIm]OPr (no propionic acid),the reaction rate of cellulose dissolved in [BMIm]OPr having 11.9 weightpercent propionic acid is slower and the DS of each sample is higherthan the corresponding sample from the other procedure. Thus, thisexample shows that, in addition to impacting solution viscosity, aco-solvent can also have a dramatic impact on reaction rates and thetotal DS obtained.

DEFINITIONS

As used herein, the terms “a,” “an,” “the,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or more elements recited after the term, wherethe element or elements listed after the transition term are notnecessarily the only elements that make up the subject.

As used herein, the terms “containing,” “contains,” and “contain” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above.

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise” providedabove.

As used herein, the terms, “including,” “include,” and “included” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above.

Numerical Ranges

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claims limitation that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

Claims not Limited to Single Embodiment

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Modifications to theexemplary embodiments, set forth above, could be readily made by thoseskilled in the art without departing from the spirit of the presentinvention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

1. A process for making a cellulose ester, said process comprising: (a)introducing a reaction medium comprising cellulose, a halide ionicliquid and a binary component into an esterification zone; and (b)combining at least one acylating reagent with said reaction medium insaid esterification zone to esterify at least a portion of saidcellulose thereby producing said cellulose ester.
 2. The process ofclaim 1, wherein said binary component is an acid or a functional ionicliquid.
 3. The process of claim 1, wherein said binary component is aLewis acid.
 4. The process of claim 3, wherein said Lewis acid ischaracterized by the formula MX_(n), wherein M is a transition metalselected from the group consisting of B, Al, Fe, Ga, Sb, Sn, As, Zn, Mg,and Hg, wherein X is selected from the group consisting of halogen,carboxylate, sulfonate, alkoxide, alkyl, and aryl.
 5. The process ofclaim 1, wherein said binary component is a protic acid.
 6. The processof claim 5, wherein said protic acid is selected from the groupconsisting of methane sulfonic acid and p-toluene sulfonic acid.
 7. Theprocess of claim 5, wherein said protic acid has a pK_(a) in the rangeof from about −5 to about
 10. 8. The process of claim 1, wherein saidbinary component is a functional ionic liquid.
 9. The process of claim8, wherein said functional ionic liquid comprises the followingstructure:

wherein at least one of R₁, R₂, R₃, R₄, and R₅ is (CHX)_(n)Y, wherein Xis hydrogen or a halide, wherein n is an integer in the range of from 1to 10 inclusive, wherein Y is sulfonic or carboxylate, and wherein theremainder R₁, R₂, R₃, R₄, and R₅ groups each individually comprisehydrogen, a C₁ to C₁₀ alkyl group, a C₂ to C₁₀ alkenyl group, a C₁ toC₁₀ alkoxyalkyl group, or a C₁ to C₁₀ alkoxy group.
 10. The process ofclaim 8, wherein said functional ionic liquid comprises1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluorobutyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium,1-alkyl-3-(1-sulfonylethyl)imidazolium,1-alkyl-3-(1-sulfonylpropyl)imidazolium,1-alkyl-3-(1-sulfonylbutyl)imidazolium, and/or1-alkyl-3-(1-sulfonylhexyl)imidazolium, wherein said alkyl comprises aC₁ to C₁₀ straight-chain alkyl group.
 11. The process of claim 1,wherein said cellulose comprises a plurality of anhydroglucose units(“AGU”), wherein said binary component is present in said reactionmedium in an amount in the range of from about 0.01 to about 100 molpercent per AGU.
 12. The process of claim 1, wherein said halide ionicliquid comprises a plurality of cations and a plurality of anions,wherein at least a portion of the cations of said halide ionic liquidcomprise imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium,1,2,3-triazolium, and/or thiazolium cations.
 13. The process of claim 1,wherein at least a portion of the anions of said halide ionic liquid areselected from the group consisting of chloride, bromide, iodide,fluoride, and mixtures of two of more thereof.
 14. The process of claim1, wherein said reaction medium further comprises a carboxylic acid,wherein said carboxylic acid is present in said reaction medium in therange of from about 0.1 to about 25 weight percent by weight of thetotal reaction medium.
 15. The process of claim 14, wherein saidcarboxylic acid comprises acetic acid, propionic acid, butyric acid,isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid,nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid,substituted benzoic acids, phthalic acid, and/or isophthalic acid. 16.The process of claim 1, wherein said cellulose has a degree ofpolymerization (“DP”) of about 1,090, wherein said halide ionic liquidcomprises 1-butyl-3-methylimidazolium chloride, wherein said reactionmedium comprises about 5 weight percent of said cellulose and saidbinary component is present in said reaction medium in an amount in therange of from about 0.01 to about 100 mol percent per AGU, wherein saidreaction medium has a viscosity of less than about 60,000 poise at 0.1rad/sec at a temperature of 25° C.
 17. The process of claim 1, whereinsaid cellulose has a DP of about 1,090, wherein said halide ionic liquidcomprises 1-allyl-3-methylimidazolium chloride, wherein said reactionmixture comprises about 5 weight percent of said cellulose and saidbinary component is present in said reaction medium in an amount in therange of from about 0.01 to about 100 mol percent per AGU, wherein saidreaction mixture has a viscosity of less than about 140,000 poise at 0.1rad/sec at a temperature of 25° C.
 18. The process of claim 1, furthercomprising, prior to said esterifying, dissolving at least a portion ofsaid cellulose in said halide ionic liquid to thereby form said reactionmedium, wherein at least a portion of said acylating reagent is presentduring said dissolving of said cellulose.
 19. The process of claim 18,wherein during said dissolving, said acylating reagent is present in anamount in the range of from about 0.01 to about 20 molar equivalentsbased on the total amount of said cellulose in said reaction medium,wherein said acylating reagent comprises C₁ to C₂₀ straight- orbranched-chain alkyl or aryl carboxylic anhydrides and/or carboxylicacid halides.
 20. The process of claim 1, wherein said cellulose estercomprises a plurality of ester substituents, wherein at least 50 percentof said ester substituents comprise alkyl esters having a carbon chainlength of at least 6 carbons, wherein said cellulose ester has a degreeof substitution (“DS”) of at least 1.5.
 21. The process of claim 1,wherein said acylating reagent is present in an amount of less than 10molar percent excess per AGU, wherein said cellulose ester has a DS ofat least 2.0.
 22. A process for making cellulose esters, said processcomprising: (a) dissolving a cellulose in a halide ionic liquid tothereby form an initial cellulose solution; (b) contacting said initialcellulose solution with a binary component and an acylating reagentunder conditions sufficient to provide an acylated cellulose solutioncomprising a cellulose ester; (c) contacting said acylated cellulosesolution with a non-solvent to cause at least a portion of saidcellulose ester to precipitate and thereby provide a slurry comprisingprecipitated cellulose ester and at least a portion of said halide ionicliquid; (d) separating at least a portion of said precipitated celluloseester from said halide ionic liquid to thereby provide a recoveredcellulose ester and a separated halide ionic liquid; and (e) recyclingat least a portion of said separated halide ionic liquid for use indissolving additional cellulose.
 23. The process of claim 22, whereinsaid binary component is an acid or a functional ionic liquid.
 24. Theprocess of claim 22, wherein said binary component is a Lewis acid. 25.The process of claim 24, wherein said Lewis acid is selected from thegroup consisting of ZnCl₂ and Zn(OAc)₂.
 26. The process of claim 22,wherein said binary component is a protic acid.
 27. The process of claim26, wherein said protic acid is selected from the group consisting ofmethane sulfonic acid and p-toluene sulfonic acid.
 28. The process ofclaim 22, wherein said binary component is a functional ionic liquid.29. The process of claim 22, wherein said cellulose comprises aplurality of anhydroglucose units (“AGU”), wherein said binary componentis present in said reaction medium in an amount in the range of fromabout to about 0.01 to about 100 mol percent per AGU.
 30. The process ofclaim 22, wherein said halide ionic liquid comprises a plurality ofcations and a plurality of anions, wherein at least a portion of thecations of said halide ionic liquid comprise imidazolium, pyrazolium,oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazoliumcations, wherein at least a portion of the anions of said halide ionicliquid are selected from the group consisting of chloride, bromide,iodide, fluoride, and mixtures of two of more thereof.
 31. The processof claim 22, wherein at least a portion of said acylating reagent ispresent during said dissolving of step (a).
 32. The process of claim 22,wherein said acylating reagent comprises C₁ to C₂₀ straight- orbranched-chain alkyl or aryl carboxylic anhydrides and/or carboxylicacid halides.
 33. The process of claim 22, wherein said acylatingreagent is present in an amount of less than 20 molar percent excess perAGU, wherein said cellulose ester has a DS of at least 1.8.
 34. Theprocess of claim 22, wherein said acylating reagent is present in anamount of less than 10 molar percent excess per AGU, wherein saidcellulose ester has a DS of at least 2.0.
 35. The process of claim 22,wherein said cellulose ester is sufficiently soluble in acetone toproduce an at least 10 weight percent cellulose ester solution inacetone, wherein said cellulose ester has a DS in the range of from 2.0to 2.5.
 36. The process of claim 22, wherein at least 50 weight percentof said separated halide ionic liquid is recycled for use in dissolvingadditional cellulose.
 37. A composition comprising a cellulose esterhaving a degree of substitution (“DS”) of at least 1.5 and comprising aplurality of ester substituents, wherein at least 50 percent of saidester substituents comprise alkyl esters having a carbon chain length ofat least 6 carbons.
 38. The composition of claim 37, wherein saidcellulose ester has a DS of at least 1.7.
 39. The composition of claim37, wherein said cellulose ester has a DS of at least 2.0.
 40. Thecomposition of claim 37, wherein at least 50 percent of said estersubstituents comprise alkyl esters having a carbon chain length of atleast 8 carbons.
 41. The composition of claim 37, wherein at least 70percent of said ester substituents comprise alkyl esters having a carbonchain length of at least 8 carbons.
 42. The composition of claim 37,wherein said cellulose ester has a number average molecular weight(“Mn”) in the range of from 1,200 to 200,000.
 43. The composition ofclaim 37, wherein said cellulose ester has a weight average molecularweight (“Mw”) in the range of from 2,500 to 420,000.
 44. The compositionof claim 37, wherein said cellulose ester has a Z average molecularweight (“Mz”) in the range of from 4,000 to 850,000.
 45. The compositionof claim 37, wherein said cellulose ester has a polydispersity (Mw/Mn)in the range of from 1.3 to
 7. 46. The composition of claim 37, whereinsaid cellulose ester has a DS in the range of from 2.0 to 2.6.
 47. Thecomposition of claim 37, wherein said cellulose ester has a DP in therange of from 10 to 1,000.
 48. The composition of claim 37, wherein saidcellulose ester is sufficiently soluble in acetone to produce an atleast 10 weight percent cellulose ester solution in acetone, whereinsaid cellulose ester has a DS in the range of from 2.0 to 2.5
 49. Thecomposition of claim 37, wherein said cellulose ester is sufficientlysoluble in acetone to produce an at least 10 weight percent celluloseester solution in acetone, wherein said cellulose ester has a DS in therange of from 2.1 to 2.4.
 50. The composition of claim 37, wherein saidcellulose ester is a non-random cellulose ester.